Collapsing second and lower level tabs collapses the entire tree

[silverwings15]

When collapsing a second or lower level tab with children, instead of collapsing everything below it up to that point, the entire tree is collapsed instead, and focus is moved back to the topmost (first level) tab of the tree.

e.g.
double clicking on this tab

results in this

Win 10 x64, PM 28.1.0, TK2 0.13.3,