BES 220-24T-PWR multicast filtering

[sticke]

I've acquired a used Nortel BES 220 switch which I want to use for multicasting A/V streams on some ports. Using IGMP snooping should prevent the streams flooding other ports, such as the ADSL router. However even when I enable snooping for the relevant VLAN, the multicast packets are still appearing on all connected ports, as shown by the RMON statistics and running Wireshark on a connected PC. The 'Multicast Group Membership Table' in the web UI does not show the PC port being in any groups.

The switch is running SW v1.2.0.002 and has been reset to factory state. I don't have the Nortel manual, but found one online for BES 100/200. This refers to enabling IGMP in the web UI Configuration > Data Services > VLANs which doesn't appear in my UI. However I have Application > IGMP > IGMP Configuration instead, and presumably the fact of this setting being present means the switch must be intended to do IGMP ?

I've tried configuring a different VLAN instead of the default, but with the same result. Also tried the Rate Limiting settings, with Multicast set to 1%, again with no effect. Would be grateful for any other suggestions.