Thank you much for your answers, Dan & Karl.  Ther are some very useful advices I didn't know till now.

After some experiments I decided (against my former meaning) to switch over to WIN with my Bryce. A main point beside the bug thing was the better render times ( as my win pc is much faster than my mac mini).

Another point : I have to update to mountain lion for several reasons and so Bryce will be lost so  or so on Mac.

THX again  & kind regards,

 

Volker