Did a little offline testing
Tanks and LVT4 : If you move the Turret, Pintle and Hull guns in different directions, then go back to the driver position, then back to the gun positions, the turret will stay the same, Pintle resets to the direction of the turret, and the Hull gun resets to straight forward.
Osti and Whirbel : Move Hull gun then turret in different directions, return to driver position, Turret same, Hull resets. Move from Turret to hull position, Hull gun stays where it is. Move from Hull to Turret, the Turret resets to the direction of the Hull gun.
Hopefully i didn't mix up the data, but I see StokesAK's point.