DLink 614+ and port mapping

I have a special network application on a PC that uses port 3290 UDP in
both directions (Client-server and server-client).
I have recently altered the configuration so that the PC now connects to
the network over the LAN (not WLAN) connection of a DLink614+.

The problem is, I can't stop the DLink from mapping the outgoing port
address to something up in the 60000 range. I've tried defining an
Application using port 3290 as trigger port and Public port. I've tried
adding a definition to the Firewall. I've tried putting the PC in the
DMZ. I've tried allocating the PC to a static DHCP client address. No
luck.
What am I doing wrong?

T.