So…I got used to live with it but I suppose it’s a bug or a strange behaviour.
When new windows appear on the screen (usually displayed images) they seem to have a predetermined pattern to appear a few cms right-down from the previous. But there is a point at which they keep going right to the point that they don’t appear at all on the screen.
Kind of the visible range of the screen wasn’t properly delimited thus windows ain’t visible or clickable so you have to click some window on the top-left and re-do the step to see the window.
I’m using Windows xp (I seem to remember it also happened in win 7)