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.
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.