[Exim] Strange behaviour

Hello to everybody,

Since the laste upgrade (Debian potato/Exim 3.12) I am experiencing
something strange.
I am running virtual Domains, and at least one user is receiving his mail as
usually if he gets it per cc:
If I adress him with To: he gets his mail into his mailbox but can`t pop it.
I am using qpopper.

Has anybody an idea of what is wrong?

thanks
markus