This is particularly visible (and annoying) when reading newsgroups. Let's say you're viewing your newsgroups in threaded mode. You open up a tree to see how many replies there are by clicking once on the triangle. The tree will open. Now, if you attempt to open the message contained on any node that has children, the tree rooted at that message will collapse. Preferred behaviour would be for the state of the tree, openned or closed, to be to auto-open if closed--but if it's already opened, to stay opened.
Confirmed using build win32 2000-112808-mtrunk. Marking duplicate of bug 56844 *** This bug has been marked as a duplicate of 56844 ***
Verified as duplicate