diff --git a/apps/demo/index.html b/apps/demo/index.html
index 3701b11e6..929d3ec0c 100644
--- a/apps/demo/index.html
+++ b/apps/demo/index.html
@@ -19,6 +19,7 @@
           <button id="diff-files">Diff Two Files</button>
           <button id="load-diff">Load Large-ish Diff</button>
           <button id="worker-load-diff">Worker Render Diff</button>
+          <button id="clean">Clean</button>
           <label>
             <input id="unified" type="checkbox" />
             Unified Diffs
diff --git a/apps/demo/src/main.ts b/apps/demo/src/main.ts
index 07085041e..f23d205a6 100644
--- a/apps/demo/src/main.ts
+++ b/apps/demo/src/main.ts
@@ -632,6 +632,15 @@ function getThemeType() {
       : 'system';
 }
 
+const cleanButton = document.getElementById('clean');
+cleanButton?.addEventListener('click', () => {
+  const container = document.getElementById('wrapper');
+  if (container == null) {
+    return;
+  }
+  cleanupInstances(container);
+});
+
 // For quick testing diffs
 // FAKE_DIFF_LINE_ANNOTATIONS.length = 0;
 // (() => {
diff --git a/packages/diffs/src/components/VirtualizedFile.ts b/packages/diffs/src/components/VirtualizedFile.ts
index d799a0f88..e83720659 100644
--- a/packages/diffs/src/components/VirtualizedFile.ts
+++ b/packages/diffs/src/components/VirtualizedFile.ts
@@ -157,6 +157,7 @@ export class VirtualizedFile<
   // Compute the approximate size of the file using cached line heights.
   // Uses lineHeight for lines without cached measurements.
   private computeApproximateSize(): void {
+    const isFirstCompute = this.height === 0;
     this.height = 0;
     if (this.file == null) {
       return;
@@ -189,7 +190,11 @@ export class VirtualizedFile<
       this.height += fileGap;
     }
 
-    if (this.fileContainer != null && this.virtualizer.config.resizeDebugging) {
+    if (
+      this.fileContainer != null &&
+      this.virtualizer.config.resizeDebugging &&
+      !isFirstCompute
+    ) {
       const rect = this.fileContainer.getBoundingClientRect();
       if (rect.height !== this.height) {
         console.log(
@@ -241,14 +246,16 @@ export class VirtualizedFile<
       return false;
     }
 
-    this.top ??= this.virtualizer.getOffsetInScrollContainer(fileContainer);
     if (isFirstRender) {
       this.computeApproximateSize();
       this.virtualizer.connect(fileContainer, this);
+      this.top ??= this.virtualizer.getOffsetInScrollContainer(fileContainer);
       this.isVisible = this.virtualizer.isInstanceVisible(
         this.top,
         this.height
       );
+    } else {
+      this.top ??= this.virtualizer.getOffsetInScrollContainer(fileContainer);
     }
 
     if (!this.isVisible) {
diff --git a/packages/diffs/src/components/VirtualizedFileDiff.ts b/packages/diffs/src/components/VirtualizedFileDiff.ts
index 80fb2160a..c8d4dc0a7 100644
--- a/packages/diffs/src/components/VirtualizedFileDiff.ts
+++ b/packages/diffs/src/components/VirtualizedFileDiff.ts
@@ -204,6 +204,7 @@ export class VirtualizedFileDiff<
     if (this.fileContainer == null) {
       return;
     }
+    this.renderRange = undefined;
     if (visible && !this.isVisible) {
       this.top = this.virtualizer.getOffsetInScrollContainer(
         this.fileContainer
@@ -222,6 +223,7 @@ export class VirtualizedFileDiff<
   // dynamically change for a number of reasons so we can never be fully sure
   // if the height is 100% accurate
   private computeApproximateSize(): void {
+    const isFirstCompute = this.height === 0;
     this.height = 0;
     if (this.fileDiff == null) {
       return;
@@ -296,7 +298,11 @@ export class VirtualizedFileDiff<
       this.height += fileGap;
     }
 
-    if (this.fileContainer != null && this.virtualizer.config.resizeDebugging) {
+    if (
+      this.fileContainer != null &&
+      this.virtualizer.config.resizeDebugging &&
+      !isFirstCompute
+    ) {
       const rect = this.fileContainer.getBoundingClientRect();
       if (rect.height !== this.height) {
         console.log(
@@ -345,15 +351,16 @@ export class VirtualizedFileDiff<
       return false;
     }
 
-    this.top ??= this.virtualizer.getOffsetInScrollContainer(fileContainer);
     if (isFirstRender) {
       this.computeApproximateSize();
-      // Figure out how to properly manage this...
       this.virtualizer.connect(fileContainer, this);
+      this.top ??= this.virtualizer.getOffsetInScrollContainer(fileContainer);
       this.isVisible = this.virtualizer.isInstanceVisible(
         this.top,
         this.height
       );
+    } else {
+      this.top ??= this.virtualizer.getOffsetInScrollContainer(fileContainer);
     }
 
     if (!this.isVisible) {
diff --git a/packages/diffs/src/components/Virtualizer.ts b/packages/diffs/src/components/Virtualizer.ts
index 2af9181c4..27fb7d222 100644
--- a/packages/diffs/src/components/Virtualizer.ts
+++ b/packages/diffs/src/components/Virtualizer.ts
@@ -37,18 +37,22 @@ const DEFAULT_VIRTUALIZER_CONFIG: VirtualizerConfig = {
 
 let lastSize = 0;
 
+let instance = -1;
+
 export class Virtualizer {
   static __STOP: boolean = false;
   static __lastScrollPosition = 0;
 
-  public type = 'basic';
+  public readonly __id: string = `virtualizer-${++instance}`;
   public readonly config: VirtualizerConfig;
+  public type = 'basic';
   private intersectionObserver: IntersectionObserver | undefined;
   private scrollTop: number = 0;
   private height: number = 0;
   private scrollHeight: number = 0;
   private windowSpecs: VirtualWindowSpecs = { top: 0, bottom: 0 };
   private root: HTMLElement | Document | undefined;
+  private contentContainer: HTMLElement | undefined;
 
   private resizeObserver: ResizeObserver | undefined;
   private observers: Map<HTMLElement, SubscribedInstance> = new Map();
@@ -146,7 +150,7 @@ export class Virtualizer {
           this.scrollHeightDirty = true;
           shouldQueueUpdate = true;
           if (this.config.resizeDebugging) {
-            console.log('Virtualizer: content size change', {
+            console.log('Virtualizer: content size change', this.__id, {
               sizeChange: blockSize - lastSize,
               newSize: blockSize,
             });
@@ -159,11 +163,11 @@ export class Virtualizer {
             this.heightDirty = true;
             shouldQueueUpdate = true;
           }
-        } else if (entry.target === this.root.firstElementChild) {
+        } else if (entry.target === this.contentContainer) {
           this.scrollHeightDirty = true;
           shouldQueueUpdate = true;
           if (this.config.resizeDebugging) {
-            console.log('Virtualizer: scroller size change', {
+            console.log('Virtualizer: scroller size change', this.__id, {
               sizeChange: blockSize - lastSize,
               newSize: blockSize,
             });
@@ -200,15 +204,31 @@ export class Virtualizer {
     });
     this.resizeObserver?.observe(this.root);
     contentContainer ??= this.root.firstElementChild ?? undefined;
-    if (contentContainer != null) {
+    if (contentContainer instanceof HTMLElement) {
+      this.contentContainer = contentContainer;
       this.resizeObserver?.observe(contentContainer);
     }
   }
 
   cleanUp(): void {
+    this.resizeObserver?.disconnect();
+    this.resizeObserver = undefined;
     this.intersectionObserver?.disconnect();
     this.intersectionObserver = undefined;
+    this.root?.removeEventListener('scroll', this.handleElementScroll);
+    window.removeEventListener('scroll', this.handleWindowScroll);
+    window.removeEventListener('resize', this.handleWindowResize);
     this.root = undefined;
+    this.contentContainer = undefined;
+    this.observers.clear();
+    this.visibleInstances.clear();
+    this.instancesChanged.clear();
+    this.connectQueue.clear();
+    this.visibleInstancesDirty = false;
+    this.windowSpecs = { top: 0, bottom: 0 };
+    this.scrollTop = 0;
+    this.height = 0;
+    this.scrollHeight = 0;
   }
 
   getOffsetInScrollContainer(element: HTMLElement): number {
@@ -245,6 +265,9 @@ export class Virtualizer {
     }
     this.intersectionObserver?.unobserve(container);
     this.observers.delete(container);
+    if (this.visibleInstances.delete(container)) {
+      this.visibleInstancesDirty = true;
+    }
     this.markDOMDirty();
     queueRender(this.computeRenderRangeAndEmit);
   }
diff --git a/packages/diffs/src/utils/createWindowFromScrollPosition.ts b/packages/diffs/src/utils/createWindowFromScrollPosition.ts
index 16ced1305..98142eb14 100644
--- a/packages/diffs/src/utils/createWindowFromScrollPosition.ts
+++ b/packages/diffs/src/utils/createWindowFromScrollPosition.ts
@@ -18,13 +18,19 @@ export function createWindowFromScrollPosition({
   overscrollSize,
 }: WindowFromScrollPositionProps): VirtualWindowSpecs {
   const windowHeight = height + overscrollSize * 2;
-  if (windowHeight > scrollHeight || fitPerfectly) {
+  const effectiveHeight = fitPerfectly ? height : windowHeight;
+  scrollHeight = Math.max(scrollHeight, effectiveHeight);
+
+  if (windowHeight >= scrollHeight || fitPerfectly) {
+    const top = Math.max(scrollTop - containerOffset, 0);
+    const bottom =
+      Math.min(scrollTop + effectiveHeight, scrollHeight) - containerOffset;
     return {
-      top: Math.max(scrollTop - containerOffset, 0),
-      bottom:
-        scrollTop + (fitPerfectly ? height : windowHeight) - containerOffset,
+      top,
+      bottom: Math.max(bottom, top),
     };
   }
+
   const scrollCenter = scrollTop + height / 2;
   let top = scrollCenter - windowHeight / 2;
   let bottom = top + windowHeight;