The different turret stabilization modes do not work properly in every case, for some reason.
What i noticed is that "stabilized" behaviour can happen for vehicle turrets that have stabilizedInAxis=0 in their config (confirmed via ingame config viewer), which means they should have no stabilization whatsoever.
It definitely happens if you enable free-look (default bind: double tap ALT) and go into exterior view. There may be more to it, i dont have the time to test every possibility.
Happens in latest dev branch update, but should also be in stable (it wasn't introduced in the last two weeks)