I tried searching for "ɣ" on Linguistics.
Rather than performing the search, it displays the blank Search page. (With the previous search, it had displayed a search help page.)
Presumably, it assumes a 1-character query was typed accidentally. However, in this case, the 1-character query is an IPA symbol (voiced velar fricative) that produces relevant search results.
As a workaround, if you search for "ɣ ɣ ɣ ɣ", it does do the search. This proves that the necessary search functionality exists for 1-character search terms.
The front-end should be changed to allow such searches.