Parent zone rejected on problems with slave zone

[Peter L]

We have a very strange problem.  Our root, corpx.com has many children
that it slaves for.  They are not delegated, but we pull the zones as
slave.  Ocassionally, when one of these zones' NS goes off line or
whatever, this child zone will expire.  Upon that event our root
nameserver for corpx.com says " master zone "corpx.com" (IN) rejected
due to errors".  As soon as we either correct the connection to the
slave zone and get a good zone transfer, or comment out that slave
zone in named.conf, the root server is fine again.  What is going on
here?

-Peter L