I have found recently countless examples of entities (recordings/releases/release groups) with tags up-voted by myself that I'm pretty sure I've never voted for. This always appears on entities for which I'had done some up-votes, but not on the tags currently marked.
First of all I didn't reported it and thought I must have clicked on some +/- up vote tags by mistake.
But this is becoming more and more frequent and it cannot be the case anymore.
The latest example is http://musicbrainz.org/release-group/2fbf4c3e-09e5-38f0-ae59-fbdc9ea16b87/tags. I'm pretty sure that I may have up-voted "hard rock" and maybe "classic rock" or "rock" if any, but nothing else. But now when I look at the release group it says that I up-voted "pop/rock" and "should be public domain" and nothing else. Two tags I never up-vote for! I may well have down-voted them however...
On all the other latest examples that I have analyzed, I was able to identify a single event that always preceded the appearance of these misplaced up-votes on tags: All these entities were recently merged. For the example above the release group was merged a few days ago in http://musicbrainz.org/edit/34427730.
I noted also until now, that the misplaced tags are always up-votes, never down-votes.
One possible explanation that I Could find is that down votes can beconverted in up-votes in a merge. I will try to track that down in other examples.
This may be a serious bug I every merge has the possibility to destroy the tags up-vote count
Please look at what is going in the merge code for tags up-votes; it is slowly destroying all the tags I've been adding
Thanks a lot.