When I am in the bz2 menus (full screen), then I press alt-tab to return to windows desktop, then by clicking on the bz2 task I return to the game : menu buttons have became unreadable and colors have became very stranges !!!
That bug doesn't happen when bz2 is dispayed in windowed mode.
Here is a video of the problem (divx 5.11 required) :
http://pingouiman.free.fr/bz2/alt-tab_bug.avi
My graphic configuration : ATI RADEON 9800 128Mo / Catalist 4.3
Simple solution: Don't Alt+Tab.
Not sure if it's really a BZ2 problem... done that many a times on my old Geforce2 MX without a problem.
I think it's an ATI graphic card issue...
Whatever, there is a solution to this problem : I only need to Alt-Enter to go into windowed mode then Alt-Enter to return to full screen mode - menus appearance becomes normal after that.