BTW, I've done a project clean but no effect.
Last time I overcame this I had to create a new, clean workspace. Assuming something in the .metadata folder got corrupted. However, as you know, that's a drag if you have lots of keys mapped or special settings to the workspace. Otherwise, it's pretty straightforward. If you don't have a lot of workspace settings, you could of course just delete the .metadata folder but then you're left with nothing if a new workspace doesn't fix it.
that helped Thanks a lot!