don't set DEBEMAIL in /etc/pbuilderrc
That's pretty much it.
The reason is that, if you do set DEBEMAIL pbuilder/cowbuilder configuration option (most likely, to the same value of your $DEBEMAIL envvar) you will end up generating .changes file containing fields like:
Maintainer: Stefano Zacchiroli <firstname.lastname@example.org> Changed-By: Stefano Zacchiroli <email@example.com>
I discovered this thanks to Ana about a month ago and it quite shocked me, since I've been using the same pbuilder (and then cowbuilder) configuration for quite a while (years ...) without realizing that.
The complicity of a missing lintian check has surely helped (wishlist bug filed) as well as a weird/buggy behavior on the *builder side (there are some bugs on that line, I just haven't taken the time yet to understand what should be the correct behavior).
Bottom line: just check whether you are screwing up .changes file due to overzealous attitude in builder configuration