FortiGate not resolving DNS

Hi.

HW is 1500d.

Firmwae v5.4.4,build1117

Problem: FG does not resolve dns queries

DNS Servers are defined in global mode (global>network>dns > server1, server2)

DNS Server are defined in VDOM mode (vdom-x > network > dns servers > Service on inside interface, Forward requests to system dns)

i do not see any requests. I try to trigger a requests doing a ping with target=www.fortinet.com from vdom-x. I have web proxy explicit configured and can only access internet with IP address entered as url.

i capture pakets on inside interface. No dns requests.

Any idea?

Thanks a lot.

Frank