Well, thanks for your efforts - imho tags should be included when I search, its the behaviour that would be expected by any sane user.
Viewing post in Make Tags non case sensitive
hmm. it could be better.
if you search for "official" tags, for lack of a better word, those come as a result as well.
but you cannot search for custom tags there. you have to put it in the tag-search box.
mahjong is not an "official" tag. try with chess to see the difference.
so maybe idea would be to make custom tags searchable in search box, should there not be a reason to not have it so. (there might. key word spamming is tactic in search ranking optimisation.)