【WPF】Dragging the merged cells will result in an abnormal cell

[Lazycat8192]

Description

If you drag a merged cell with content up or down into an area of unmerged cells, an area of blank cells appears that does not appear to have been merged. But when clicked and edited, the area has the characteristics of a merged cell.
如果将一个带有内容的、合并的单元格向上方或下方拖动到未合并的单元格区域，将出现一个看起来没有被合并的空白单元格区域。但是点击和编辑该区域时，该区域具有合并的单元格的特性。

If you try to merge or unmerge the abnormal cell, will produce a "System. NullReferenceException" error
如果尝试对这个异常的单元格进行合并或者取消合并的操作，将会产生“System.NullReferenceException”错误

To Reproduce

1. Write anything inside a merged cell, empty cells don't get this bug
   在一个合并单元格内随便写点什么，空单元格不会出现这个bug
2. Drag it above/below an unmerged area
   拖动他到一个上方/下方的一个未被合并的区域
3. See error

Screenshots

Operation display

Merge and unmerge errors：System.NullReferenceException

Edition

• WPF

Environment

• OS: Windows 10
• Language of OS: Simplified Chinese