I noted that since a couple of days the updates to DNS have been stuck and it caused a problem with out local DNS server as well. After investigating it appeared that an invalid name has been added to DNS by someone:
dhcp-44-149-72-.db0eif IN A 44.149.72.89
Note the trailing minus sign in the name, which is not allowed. Bind with (default) strict name checking will issue an error on this, and (I think that is bad) it will refuse to load or transfer the entire zone. So the previous version of the zone will remain active. This was version 2001012115, while the current version is 2001050245 so it has been stuck for a couple of days (the format used for the version is YYMMDDHHMM).
For now I have deleted the bad name, but it would probably be prudent to add:
check-names warn;
to the zone configurations of the bind daemons running the ampr.org zone so that they have the more reasonable behavior of just ignoring that single name instead of the entire zone.
Rob