Found solution, need explanation :)

[Mats Fredholm]

Hi folks,
with a setup of a caching bind (9.2.3 & 9.3.2-P1) servers I had configured
to use option 'query-source address * port 53;' to be sure not to 
stumble into
problems with our firewall.
I took long time for me to find out that this was instead causing problems.
The cacheing server is NAT'ed with no open ways from outside to it,
but surely asking a question it should get a reply?
Querying some servers, I did not get any reply, most worked fine though.
(saw (snoop) queries sent out)
There is probably a simle explanation here? RTFM?

TIA,
Mats