UDP, source ports are still being modified by the F5,

we have an issue with an application and basically during the set-up of the connections it makes both TCP and UDP connections via a Socks Proxy.

However, it appears the F5 is modifying the source UDP port before forwarding onto the Proxy (which is used as the 'destination' port) so is then being dropped, and the connection fails (we only allow 48129-48192).

What I would like to understand is; can we forward on the UDP packets without apparent modification to the ports?