Questions about Boioi migration

I'm playing a campaign with the Boioi, and recently captured Patavia (Can't remember the actual name). Since it was low on western tribal culture (once again, the actual term escapes my mind) I thought I'd build a migration government there to try and reinforce my culture in the area as well as to just try things out.

I can't build it there.

In fact, the only 'factional' government I can build there is Protectorate. It seems odd, since the description for migration government says it can only be established in areas where western tribal culture is still the minority. Oddly enough, I can build migrations on my starting regions and other areas that are already mainly western tribal, though this shouldn't be possible according to the building's description. It's almost like a line of code was inverted or something...

Is this a bug, an incomplete feature or that way by design? I hope you understood what I tried to say. Everything else seems to work just fine expect for the mission to assist the folks in Felsina, at least if the Romans don't actually capture it when they attack.

Ah crap, I missed the "less than 50% ETS" edit to the requirements in the Boii Migration building, when I did all the others. I'll fix that, but in the meantime you'll have to build a Protectorate until the level of rel_e rises to 25%.