Do you know what causes this?

[prinsipe]

I'll be glad if someone enlightens me about it, thanks in advance...........

 

[Geffy]

The application in the background which had edges which match the edges of the fup up, would be the cause, its not yet released its display area on the gfx card or some such like that. So it just gets painted over poorly as no new display data has come from that program to render.
Usually happens when a program terminates abnormally or on seriously bad bloated software, I often had this problem with Creative PlayCentre, which imho is the most bloated piece of software availible, though I could be wrong.