That's a nice video, thanks. Have to try with some nades picked up from ground next, I'm pretty sure I got mine from armory last time. Maybe there's a better chance of replicating it like that.

Cool, got it fixed, thanks for setting me on the right path! The moment of starting to throw a grenade doesn't update the skeletal pose on the server (unless a server player has the client player in the camera view - with a dedicated server there is no such thing as a server player). So, after leaving a vehicle and throwing an impact nade before anything else causes the skeletal pose to be updated, the skeleton will still be inside the vehicle and the grenade will be spawned inside the vehicle, the grenade being an impact nade it blasts on the collision before the skeletal pose would be updated on the moment the grenade is let go and thrown (which is why it doesn't reproduce with hand grenades). Didn't try C4, but I'd imagine the same issue there, the C4 will spawn and stick to the vehicle.

Some events cause the skeletal pose to update, i.e. shooting or bullets being shot close enough, which can explain why it doesn't reproduce all the time. Joining with one RWR to another playing PvP quick match with 0 bots had the issue happen 100% with closed vehicles as long as the client was nowhere near the server player.