Use caps for JIDs without a resource part
Gajim doesn't process caps for JIDs that have no resource part but it should do that:
The disco#info request is sent by the requesting entity to the generating entity. The value of the 'to' attribute MUST be the exact JID of the generating entity, which in the case of a client will be the full JID <email@example.com/resource>.
Steps to reproduce
Send caps from a JID without the resource, the features will not work.