multicasts are not forwarded on wifi interface

[Hooshang F]

Hi,

We have a freebsd 8.3 wifi-AP running as a VirtulaBox guest
with 2 ethernet (em0 & em1) and one USB wifi interface (wlan0). Everything
works except that multicast packets arriving on wlan0 interface are not
forwarded on Ethernet interfaces. Also, multicast packets arriving on
Ethernet interfaces are not forwarded on wlan0 interface (however,
multicasts are forwarded between Ethernet interfaces). As a result,
portable devices are not able to discover
DLNA media servers using UPnP.

The kernel is compiled with MROUTING option and mrouted
is running with default configuration.

Any points/hints is appreciated.