>> It was being caused by my email client "Zimbra",
- I doubt it. I have that exact same problem, occasionally, exactly as you describe. And I've never heard of "Zimbra" and certainly don't have it on my PC. I used ZoneAlarm Internet Security Suite until a couple of months ago when I switched to Kaspersky and you know what .. .. I can't recall seeing this problem since.
This is SUCH A BIZARRE problem. I have tried, unsuccessfully, to describe it to others and I'm sure they think I'm crazy. Their eyes glaze over and they lose interest in what I'm saying. Then I'm offered trivial 'solutions' which are nowhere near the mark.
Zimbra, ZoneAlarm .. maybe it's something to do with programs starting with "Z". No, seriously.. at first I used to reboot the PC to cure it. Latterly I discovered that if I just shut down every app I have open it can correct itself. Thanks for the browser tip. Personally I think it's some accidental key combination I hit.
Alec.
Ascot, England.