I have this same issue with both v14 and v15. Not only does it cause everything to freeze. I also get repeatedly disconnected from RDP and then often cannot reconnect for several minutes. It is extremely frustrating. My productivity has suffered greatly because of this especially before determining that PL/SQL Developer was causing this. But now at least I know I can shut it down to resolve the issue.
When this occurs, other applications always unfreeze before PL/SQL Developer.
