When a popup menu is opened (for example with C-mouse-1 or S-mouse-1)
and closed by clicking somewhere else, it seems like an extra mouse
event is sent.
This can cause the point to be set, the region to be removed or
extended and what not - all of which is undesirable and unexpected.
Also, there seems to be something more going on than just a single
mouse event that is sent.
If you fill a buffer with text, set the point in the upper left part,
move the mouse cursor to the lower right (over text, position "A")
and do a S-mouse-1, the font popup menu opens. Then, mouse the mouse
to the lower left (over text, position "B") and click mouse-1. What
happens for me is that the text is selected from A to B gets selected
(and the point is moved).
This is with a build from today's CVS.