The 40mm seems to have trouble penetrating vehicles with thin armour. It bounced off m3's and m8's no matter the angle. It is very scary seeing tracers bounce off heading directly verticle in the sky. I generally attack gv's from the rear in a near verticle dive- it's odd that it isn't penetrating.
Although i've no idea if this is a bug or not- the t34 seems pretty immune to 40mm too. I don't know what the thickness of the top armour so i don't knwo whether it should be able to be penetrated or not- but it's very, very difficult to penetrate.
