multiple null sinks mix up ports

I tested out the Virtual sources and improved null sinks at commit 3c2ab98a So far seems to work really well with one null sink.

But when using two null sinks at the same time, i.e.:

pactl load-module module-null-sink sink_name=sink_a object.linger=1 channels=2 media.class=Audio/Sink channel_map=FL,FR
pactl load-module module-null-sink sink_name=sink_b object.linger=1 channels=2 media.class=Audio/Sink channel_map=FL,FR

Audio routed into the inputs of sink_a exits on sink_b and vice versa. I'm using catia to connect ports if that matters.