Sometimes (quite often) the tall grass on Altis absorbs all damage directed against vehicles inside it. Eg. placing a heavy satchel under light vehicle and detonating it results in the given vehicle taking no damage, as the tall grass absorbs the whole energy of explosion.
This has become a major issue in eg. TvT mods with MHQs, as players place the MHQs (respawn points) inside the tall grass, which makes the MHQs undestroyable in practice.