Version:           1.9.6 (enterprise 20070904.708012) (using KDE 3.5.7 "release 72.2" , openSUSE 10.3)
Compiler:          Target: i586-suse-linux
OS:                Linux (i686) release 2.6.22.12-0.1-default

When I right click on a message and choose "move to" and begin navigating the folder tree, some of the folders I open are two column folders.  When these open to the left, and the second column list is short, there is a blank area alligned with the parent window.  Moving the mouse from the parent to the column on the left, causes the child window and the parent window to close and brings me back to the right-click menu only.

The problem is that it can be difficult to get the mouse moved over to a valid(non-blank) area of the child without triggering the close action by having the cursor over a blank for too long.

It appears to me that the problem is in how the blank space is handled.  Mouse over the blank space should not cause the close any more than mousing over a valid item in the list, and "selecting" the blank space should have no effect as well.  Only selecting a valid destination or another window should close the child menu.