Slitherine

I was fighting against the Boruvians and Imperial Garrison units ( which aren't meant to be able to invade other provinces) were invading me in full armies. They're not that hard to beat (except when they're accompanied by Hussars, greatswords , etc) but very, very tedious to have to fight endless armies of them.

That is a bug.

I think i was maybe confused here - Borvuian empire was invading me, but i was counter-invading them afterwards too.