I'm having a similar problem with email addresses for a recently moved domain. I initially assumed it was a DNS problem, but querying ns[1-3].dreamhost.com with 'dig' shows that ns2 and ns3 are happy, but ns1 claims there is no MX record.
dnsreport.com was showing that ns1 seemed to be running a different dns daemon; ns3 seems to be timing out...
188.8.131.52: "Served by POWERDNS 2.9.20 $Id: packethandler.cc 539 2005-11-11 11:17:47Z ahu $"
184.108.40.206: No version info available (timeout on lookup). Could be tinydns 1.00 through 1.04.
It also reports that the SOA serial numbers for ns1 is different. If ns1 is less up-to-date than the others (which seems to be the case), then surely it shouldn't be listed as the primary nameserver?