only the response has aa flag can be cached?

[pyh at mail.nsbeta.info]

> These triggered the release of 9.7.2-P1
> when we were rejecting these after tightening the response processing
> to treat glue to answer responses as referrals to address the issue
> of named return glue records from the parent zones rather than the
> actual answers in the child zones.  

Sorry I'm not the english speaking people.
What does this statement mean? 

Thanks.