This bug occurs when the 'Apply' button of the opened Messenger Plus! Live Preferences panel is in front of another opened window (e.g. IE, Windows Explorer, Opera etc..).
Now, when the 'Apply' button is clicked repeatedly as fast as possible, the Preferences panel
slips behind the opened window.
take a look at the Screenshot
Messenger Plus! Live 4.01.0.240
Windows Live Messenger 8.00.0792
Windows XP Home - Service Pack 2
AMD Athlon 64 X2 Dual Core 3800+
1.00 GB RAM + GeForce 6600
(just for those who are interested )