On holiday again, will come back soon like before. The must be something "loose" in the display code for this or what? It's a common thing for most ppl here.

the last (and second) time this happened to me, i did a ridiculously thorough investigation, since it just seemed so *weird* of a thing to happen, and what i discovered was that in the prefs.cfg file, my window position prefs were set to something either off my bottom-right screen corner, or close to it (i don't remember exactly) which i had never noticed because of keeping the screen maximized... you might want to check these prefs if you also keep you screen maxed:

user_pref("kmeleon.display.XPos", 0);
user_pref("kmeleon.display.YPos", 0);

(they seem to stay at zero in the recent beta versions, eliminating this problem.)