iax2 mediaonly

I have one pbx in a flash new installation, I’m using it for developement purposes.
this pbx only has 2 iax2 extensions created, 101 and 102.
everything goes fine, I can call from 101 to 102 and viceverza.
the problem is all the udp traffic goes always trough the pbx.
no matter if I use transfer=no, transfer=yes and transfer=mediaonly, always all the packets goes trough the pbx.
I’m using disallow=all and allow=ulaw in iax.conf.
call recording is disabled.
I need to test the iax mediaonly functionallity, because in my production environment, I’m using asterisk 1.2 and mediaonly is a feature only available in 1.4, so the idea is to test it and if everything is ok, move from my 1.2 to this new 1.4 version, but I need to make sure before upgrade.
what am I doeing wrong?
what parameter should I check that can be avoiding from me to transfer the packets directly to the end to end point?
firewall is disabled, in this testing machine.
any ideas…?