Multicast on a machine with bridged interfaces - how to solve the problem?

Question

openvpn

There are 3 machines on the network, on all Debian 6:
10.1.1.2 with OpenVPN up in bridge mode (the bridge is between eth0 and tap0).
10.1.1.3 is on the same physical network as 10.1.1.2.
10.1.1.4 - remote VPN client.
Testing multicast via iperf:

iperf -s -u -B 224.1.1.1 -i 1 #listener
iperf -c 224.1.1.1 -u -T 32 -t 3 -i 1 #sender

10.1.1.3 and 10.1.1.4 all send successfully regardless of where the listener is running.
But from 10.1.1.2 everything is sent, but it does not arrive anywhere, even if the listener was also on 10.1.1.2.
Tell me what could be the problem?