When a certain NS gets asked "what's the A of sipfs02.example.com?" it gives back the RR I need. But if I ask first for "the AAAA of sipfs02.example.com", it gives back an NXDOMAIN instead of NOERROR. And then the NXDOMAIN gets cached for the following query.
I'm running bind9. I searched for DNS AAAA and BIND AAAA, but got no interesting results. Got one about patching djbdns to "poison" all NXDOMAINs, but I want to kick only one particular server, not everyone.