Loop Tempo Issue


I have a very interesting issue, which I’ve never met before but now I’m facing it with my Cubase 6.

After a while the loops in my projects are starting to loose tempo just a bit slightly and its not the matter of musical mode / time stretch .
If I stop the project and adjust the loops by applying time stretch back and forth it works again perfect but only for a limited time again. Obviously it is really annoying so I hope that there is a solution around!

I have Cubase 6.0.7. and running on OS X 10.6.8.

Thanks for the help in advance!