Okay, I've found something nice:
After opening service bay (where monoprop tanks were hidden) everything started working. I felt pretty stupid at this point, I'd never expect that closing a bay cuts fuel flow from inside. So I've made some tests, and I got it.
For some reason, putting rcs thrusters on the top (or bottom) edge of 2.5m bay renders them useless when bay is closed (as they were inside), and this is not the case of 1.25m service bay (they always work while outside). This is not intended, right?
For me, the problem is kinda resolved (I can maneuver with doors open), though it would be nice if this was fixed in next versions of KSP. (Also, it would feel awesome to actually contribute something to this game!)
Thank You very much for Your support, have a nice one.