Tristan
Not sure if this helps, but I once had similar “interface connection confusing issues”, but not related the your macvtab.
What I discovered was that mt RED interface in the “Zone Configuration” was showing NONE NONE NONE for my cards, whereas the GREEN and BLUE where correctly pointing to their appropriate interface, and showing NATIVE.
When I changed the RED to point to its appropriate interface, I lost all conectivity to the internet.
So as it turns out, my issue was that I had assigned a different pseudo mac address on the gui “Network → Assign Mac Address” , which was not showing up on the “Zone Configuration” menu. May or may not be related to your issue, but may be worth taking a look.