[mod_python] auth_digest and mod_python give "Bad Request"

Hello list,

I'm trying to set up Apache 2.2.3 + mod_python 3.2.10 + mod_digest to 
provide a .htaccess protected area.

Apache and mod_python work fine just as they do, but as soon as I 
protect a directory via a "AuthType Digest" directive, authentication 
works but as soon as a user is successfully authenticated, I receive:

 >Bad Request
 >Your browser sent a request that this server could not understand.

The logs do not show anythign abnormal. What might cause this?

Thanks in advance,
Johannes