"specify" or "specifies"? [duplicate]
Your sense is correct, but as I see you've determined, this answer correctly indicates that both are used, and both are acceptable (even if some of us think the subjunctive is more natural, and would never say otherwise).
Long live the subjunctive!
http://grammarist.com/grammar/subjunctive-mood/
https://en.wikipedia.org/wiki/English_subjunctive