Are you using it for a WSGI script? If so:
The SetEnv directive will not work as it only sets per request variables in WSGI environ dictionary and not process global os.environ.
Source
Well, this took me way too long to figure out. I was trying to use multiple environments for Trac and I was using its WSGI script. I just switched to the fcgi version and everything's fine now.
I'm off to bed. I'm so gonna hate my day tomorrow...
