Non-transfering zone

[GeekGrrl]

Is there a reason why a zone would not automatically be transfered to it's
secondary nameserver after a change, serial increment, and hup on the
primary, and a hup on the secondary?

I have a zone with this behavior. My error logs on both machines contain
nothing on the matter, and the zone is formatted correctly for BIND 8. The
zone will transfer with a manual named-xfer command at the shell prompt.