NIKOLAJ82 solved the problem 2 years ago people :
[quote]Often times Windows will refuse to hide because it mistakenly believes there is still a tooltip balloon open. (I see this a lot myself with APC's Powerchute Personal Edition.) Unfortunately the only way to get your taskbar to properly hide again (and
I don't mean uncheck the "Keep the taskbar ontop of other widows" option for a quick fix) is to restart the machine so that Windows resets the tooltip balloon status. What a pain!
Thankfully through my inability to let it go and hatred for this problem I have written a file that will fix this! (Works great on my Vista machine!) All the program does is overwrite the phantom tooltip balloon and then clear the tooltip balloon and Tahdah!
The tooltip will stay up for 10 seconds so that you can read the info on it (just telling you what it does and how you can contact me if you have any problems). You can close this tooltip balloon like any other by clicking on it, or if you mouse over the program
tray icon it will close itself instantly.
http://www.multiupload.com/94SQZ50YK0
And here is a pic of how it looks in action.
http://i44.tinypic.com/1hzzn.jpg
I really hope this helped.[/quote]
Just download the software via multiupload-link and run it... it solves the problem!
This is a Microsoft bug as windows forgets that the balloon tip is not there anymore.