I just discovered the cause of an odd bug on many of my apps that I'm building under 18r1.1. If you expand a folder, add the children for that expansion, and then collapse the row, the listbox's LastIndex does not decrement to the collapsed row count.
For example:
Hierarchical ListBox with 3 Folders
LastIndex = 2
Expand one of the Folders and add 10 child rows
LastIndex = 12
Collapse the Folder
LastIndex = 12
Nothing that I do can get the LastIndex back to 2.
Mac OS 10.12.6, 10.13.5, and Windows 10 at this point.
Anyone else?