This has to be a bug and not a feature.  
I was at an airbase last night A9 I believe. Had worked my way to the edge of the field and was deacking in an M4-75.  I parked right next to a fuel tank that was intact.  An auto-ack tracked my m4 and when I tried to slew the tank to see more ack the m4 brushed the side of the tank.  The m4 was then slid in and out of the tank a few times and the 2nd track was hit by ack.  The sliding stopped with the m4 completely inside the tank, both tracks out.  I shot a few more ack and buildings, a plane or 2 then decided to see if the tank was destroyable from the inside.  Since the walls of the tank were invisible except for the ladder and a few pipes, I fired 2 HE into the pipes and the fuels tank walls collapsed and caught fire.  I couldn't fire out since the walls were too high for the barrel and the 3-4 tanks circling the fuel tank tried to fire in but kept hitting the walls. I don't know if AKGreyga upped a plane and dropped a bomb in the burning tank or found a spot he could finally fire through, but finally killed my m4. While it is fun driving the enemy nuts not being able to kill you, it's still a bug that should be addressed.  Can they take out the status of non-tree objects to stop a tank or flip it like AH2 did instead of treating it like trees with the ice skating sliding  ?