Ok I will write it up and post it.
But, it is clear to me that there is one of two problems.
1) a DNS issue on Strongbolt/bluquartz, although I doubt it as zentyal dont masquerade the webserver on DMZ bot does on LAN, clearly the same DNS error cannot give those two different results.
2) The default Iptables on zentyal is different for two internal nics creating the discrepancy.
Iptables is a pain and errors are easy to make, i wont be surprised if that is the case and it sure looks like, but it will be nice if it is just a simple DNS error.