I don't think that anyone has been able to reproduce the issue.
This is not correct. I can produce this issue whenever I like to, after I updated from 5.02 to 5.12. I just have to run my copy of Winamp for a few minutes and open some windows, and soon I get the same effect as schaggo reported. I did not make out the trigger so far, but I found out that the problem is related to the modern skin, as the the classic skin works fine, even if the issue already occured on the modern skin.
So first I thought the issue could be caused by some of my installed plug-ins, as I only made an update of my Winamp and not a clean install. At this time I also get Windows exeptions after this issue occured. So I made a clean install, meaning uninstalling winamp via system-controls and manually deleting the hole Winamp directory and the "winamp.ini" within the Windows directory. So far I only installed the German Language-Pack, but the issue remains (apart from this the Windows exeptions are gone).
So I will now make an clean install without the German Language-Pack to see, if this could cause the problem. As schaggo is from Switzerland, he might also have installed the German Language-Pack.