It's not broken, for me at least. I've heard a lot of people complain about the search function but, I've never really had any major issues since 2013 and I do use the search a lot.
Results returned when searched "cga" (ignore xpaint):
If you ever run into this problem again don't use the abbreviation but, the full name. It will return more accurate results, because all it's doing is searching key words and "CGA" could be used in multiple words and usernames which would then return non expected results.
Or simply use google search with site:bitcointalk.org as a filter.