IGMP Proxy and STB

Hello.

I have one trouble with using IGMP Proxy and STB (Set-to-Box) for IPTV.
Settings: WAN Interface - Provider local network
STB Port: master-port to WAN Interface
IGMP Proxy: Upstream - WAN Interface, downstream - only port for PC (using IPTV player)

STB good working with IGMP Proxy ON or OFF, but in statistics I have 3.0 Mbps with OFF IGMP Proxy and 6.2 Mbps with ON IGMP Proxy.

Is it normal that with IGMP Proxy ON traffic to STB double?