Comment 2 for bug 734609

This is indeed a syntax error in the /etc/apt/preferences.d/official-package-repositories.perf file, where o=Ubuntu is mistakenly written instead of o=Debian.
Since LMDE is based on Debian, Mint packages should take priority over Debian packages, not Ubuntu.

I suppose adding a fix to one of LMDE specific packages can easily fix this issue.