Tvheadend

I have an IPTV network that I'd like to go through a specific network interface. For each mux, I've gone into the advanced settings and specified the specific interface, but upon testing it doesn't seem to respect the network interface I've specified. I've tested this by blocking network access on the specified interface, yet the channel still plays when I open it. I've looked into network traffic, and the muxes all still prefer the primary network interface and never use the one that I've set. Any ideas on what I'm doing wrong? Many thanks for any help you can provide.

EDIT: Running tvheadend 4.3-1875~g1c67c04c8 on Ubuntu 18.04