Steps to reproduce
Make an item with children. Collapse the item. Add a new item underneath it (at the same height). Using
tab (or other shortcut/command) move the item underneath the collapsed item above.
The collapsed item stays collapsed, and the item below just moves into the parent item. This is the behavior if you were to manually drag and then hold below and to the right of the parent item, placing it underneath the parent item (i.e. there’s UX precedence for this behavior).
The item is moved under the parent, but the parent item now becomes uncollapsed.
Chrome, ChromeOS. Probably all platforms but haven’t had the time to test.