If a turret has no stabilisation, either set in config with stabilizedInAxes = 0; or with the enableGunStabilization script command, it is forced into a stabilizedInAxes = 3; state when turned out in a turret with isPersonTurret = 1 set.
In the repro example mission attached the slammer tank has had its stabilisation disabled with the enableGunStablization script command, but again this occurs with config set examples too.
Repro instructions:
You will already be turned out and the AI is in a loop of turning left and right. Observe the commander machinegun rotating.
Turn in and the turret stabilisation stops.
Turn out and it's back to being stabilised.
tank enablePersonTurret [[0,0], false]; in debug will disable the FFV and the turret will go back to being unstabilised regardless of turned in/out state
Despite the turret itself becoming stabilised, it does not 'stabilise' the FFV unit, so I'm unsure why this is happening.