Thanks for the help

[King, John (Greg) (OAO-HOU)]

It turns out all the headache was not related to the nameserver directly.
The company has a pretty large network and it turned out that it was a
routing issue that was indirectly associated with the A records i needed to
recieve from another nameserver providing the records for the MX entries.
Figured that out after getting eye-strain looking over the many BIND cache
dumps I created.

Network folks made a change and everything works for those 2 hsc.com MX
records again. 

Greg King