asterisk users - Apr 2015 - Asterisk 13.3.0 IAX trunk issue with Yeastar

Hello,

I have a weird problem between Asterisk 13.3 and a Yeastar U200 pbx over IAX
trunk.
Should I call from Yeastar to my asterisk 13.3 the call goes through without
issues.
Should I call from asterisk 13.3 to Yeastar I can hear a ring tone however
the yeastar does not show any activities.
On the yeastar I initiated a debug command        iax2 set debug peer "my
trunk name" 
While I hear the ring from my side nothing appears in the debug of Yeastar
pbx.

On the asterisk 13.3 debug terminal I see that the call was initiated .


Same setting is working between an asterisk 13.2 and the Yeastar.
Can anyone help ?

I will try IAX trunk between Asterisk 13.3 and asterisk 13.2 to check if it
works.

Regards
Toufic