Why different search results are returned from webservice and site:
http://musicbrainz.org/ws/2/tag/?query=rock&fmt=json
http://musicbrainz.org/ws/2/tag/?query=tag:rock&fmt=json
https://musicbrainz.org/search?query=rock&type=tag&limit=25&method=indexed
Is it bug?
Not exactly a bug, but it seems the website is still redirecting to the direct database search automatically when searching for tags. We used to do this because we didn’t have an indexed tag search, but we should probably change that now 
I’ll add a ticket.
2 Likes
Search results from the site are much more correct than indexed results from the webservice. For example, the site finds the requested tag “rock” in the first result, and the service finds first ugly “rock_pop rock_rock_pop rock_rock_pop rock_rock”, but does not see simple “rock”. And why different search results are from same webservice requests: query=rock and query=tag:rock?