How can I block transmit of multicast to the wireless interface on a Time Capsule ?

I have just installed a new 4th gen Time Capsule in my network,

acting as Wireless Access Point and being a simple "bridge".

Within the same network I have a "T-Home Entertain" (german Telekom IPTV) set-top box,

which receives IP-TV via IP-Multicast from the Internet and over the LAN network.

The problem is, that as soon as the receiver is turned on, the WLAN stops working,

as it is flooded with UDP/Multicast packets. You do not even get a DHCP lease over WLAN.

As soon as you turn of the receiver WLAN is working fine again.

Is there a way to stop TC from bridging Multicast packets to the wireless interface or even

better is there IGMP support to selectivly join interface to multicast streams ?