I've looked through the Trello and didn't find this anywhere:
When performing a search, you get the results divided up into categories - Artist, Album Artist, Album, Song, Genre etc. (This is very nice, by the way)
Results in the Artist or Album Artist categories seem to be correct, but results will appear in the Album or Song categories even when the search term does not occur in the relevant tag.
For example, searching on the word "Brown" will give these results:
Artist - Havana Brown, James Brown, Ian Brown, Billy Brown etc. (all correct)
Album Artist - James Brown (again, correct in my case)
Song - Brown Sugar, Baby Brown, Soul Power, Dolphins Were Monkeys (...and many more. Some are correct, but Soul Power only appears because the artist is James Brown, and Dolphins Were Monkeys appears because the artist is Ian Brown)
A similar thing happens with the Album search results. Albums which include songs that have "Brown" in the artist name will sometimes appear, even though the album name itself doesn't have "Brown" in the title.
I know for sure all the tags are correct so I'm assuming the search feature must be picking up on tracks where the search term (Brown) appears in the filename, rather than just looking in the relevant tag field? How it applies this to album results is a mystery.