IPTV/multicast floods wifi interface

[andy.nl]

Dear experts,

I have a opnsense box as follows:
WAN: iptv/internet separated by vlans (via FTH)
LAN: local lan, including one IPTV receiver
WIFI: guest wifi, separate subnet from LAN. Wifi card is built into pfsense box

Everything is running well, except:
When the IPTV receiver is on and receives broadcast (via multicast and IGMP proxy in opnsense), then it seems that all multicasts are also sent to the wifi interface and not only to the LAN.
This obviously floods my guest wifi with useless data, as there is no IPTV receiver in the wifi.

I have no clue why the multicasts are also directed to the wifi and not only to the LAN, because in the IGMP proxy there is only entered the LAN subnet.

Has anybody an idea how I can block the multicast packets from entering the wifi interface?

Thanks for your help in advance,
andy