Your local entries look fine, at least the IPv4 that I looked at. Nothing
really tricky there. Your serial number of the file is a little old (2006),
but that should not matter (I use the same format as you do).

I did not see the "default-zones" file. I am hoping you are not conflicting
the "mtu.net" domain (with this mn.mtu.net named) through that file, but I
do not see how that would create issues with resolving outside hosts.

Sorry, I am no help.