How to reproduce (with latest cvs or 1.1):
(1) Create a topic with a comma, e.g. "a,b" in the
    demo tracker. 
(2) Create an issue and assign the topic to the issue
    -> error message:
    "property topic: 'a' is not a keyword"

I originally discovered this bug in a production
tracker with sqlite as backend so it seems to be 
backend-independant.

Regards,
David