[outages] Google Resolver 8.8.8.8 Selectively responding to RDNS requests

I have a /24 in an Internap colo and use Google Resolver 8.8.8.8 on all my machines. Google will not consistently respond to RDNS lookups from source IP X.X.X.1 but will respond consistently if I change the IP address of the machine to X.X.X.2. I have proven the DNS response is never returned using tcpdump. It's positively not a local networking issue as changing my resolver to 4.2.2.2 (Level 3) while the machine uses X.X.X.1, the RDNS responses arrive without fail. Has anyone else seen this sort of selective response by Google? Do they maintain some sort of black list?