Sounds like a problem with serial numbers. Close to the top of the zone file, you'll see a serial number in a line that looks something like:
domain.com 3600 IN SOA ns1.domain.com. root.domain.com. (
2006112200 7200 3600 1209600 3600 )
That 2006112200 is the serial number. The standard is currently 4 digit year, 2 digit month, 2 digits day, then 2 extra digits as a subversion.
Any time you make changes, you need to update the serial number. As long as it is at least 1 number higher, it will be updated. You will probably need to be root to change the domains, unless it is a customized bind install.