Firewall/NAT

Does the m0n0wall NAT firewall create state for UDP connections which are initiated from the LAN to the WAN, such that the same external UDP port can be used to send data back to the LAN client?  We have an application which uses UDP "heartbeats" to create a "NAT hole" for the WAN-side server to communicate back to the client which works on all the SOHO and residential routers we have tried, but m0n0wall will not let the UDP packets back in.  Is this a configuration problem, or does the core m0n0wall firewall/nat not support this?