I've noticed several times now, that despite the greatly improved vehicle handling, targeting is still somewhat borked.
My experience is mainly with Eldar vehicles, so feel free to add observations for other factions.
Issueing a move order, such as when backpedalling from incoming enemies, will automatically cause the aquiration of a new target by the game A.I., which is often annoying, but sometimes downright frustrating.
Having a Fire Prism discharge its blast at a squad of rippers when there's a Fex coming in, or having a Falcon switch to a fresh squad of sluggas when the half-dead Warboss is snapping his claw in front of its nose is certainly bloody stupid.
Also, this means that e.g. the Fire Prism charge up is cancelled, delaying firing significantly. On top of this, gun turrets appear to turn very slugishly, enhancing the feeling of being pushed out of control.
I understand that vehicles are considered very powerful, now that they handle so sleekly and any further buffs need to be careful.
Therefore I suggest that vehicle main guns cease fire for a brief time when accelerating from standstill, but in turn do not auto-retarget.