My hint is to slide out keyboard (display will rotate home screen of HTC touch flo) and to put device to sleep (and probably close slider back to normal, it will keep sleeping). Try to have it like this one night and than turn display on. You will notice that icons and mainly white text of phone or action button at botton left (upper left) will be "burned-in".
Imho the burning process (or persistent image process creation) is also active if device is in sleep mode. Probably some bug in drivers, or graphics card? Do someone else have noticed this behavior?
Also when you immediately restart phone, you can see that persistent image in boot screen. So it is not sw problem, but hw, like written in previous posts.
PS: I dont see the bug, I see just telephone with some OS which has more bugs than hardware problems
