Strange Nuendo/Cubase Crash


Im Using: 
- MAC OS 10.8.5
- XCode 4.6.3 
- Nuendo 6 - 64bit
- Reaper 64bit

I think I have the same problem as some others with my Plugin. 
When I load my Plugin in a Track, everything is fine.
When I close the Editor of the Plugin before unloading, everything works fine. 

But when I unload the Plugin, the Host stands still till I kill the host manually. I attached it to XCode, but I cannot get any meaningful error-message. 
The problems occur only in Nuendo, in Reaper the Plugin/Editor works fine and nothing crashes. 

Now I hope that maybe someone has an idea?