Thank you nomuse.

I must admit your workaround is a bit too complex for me. I switched back to SR 1.1. I just installed the SR1.1 pack again and the Import-function is working as expected. Until know (just a few hours of testing) there seems to be no instability. I'll let you know if I experience problems.
Thank you again for your quick response.

Thank you nomuse,

I saved my work as a scene file. It saves as *.pz3 and also the *.pmd and the *.dyn files are saved.
Then I tried to import this file into another scene. That worked perfectly well before I installed SR2 and it works still in P6.

Following your workaround I still have a problem. How can I set the timeline to zero without loosing the pose of my character?

I also confirm the delete-bug is very annoying. Even the menu  "Object ->Delete Object" is sometimes greyed out and therefore NOT working.

I also found that the window showing the rendered image after rendering (Pressing button ) has lost its scroll bars. So you can´t see the rendered picture