That's hilarious! I'll ensure damage is blocked if a player is 'dying', and I've also added something for the next update already that mitigates players having the ability to enter vehicles while downed (although wouldn't have fixed this situation really).
I used to freeze players while they were downed which fixed issues like this, but it meant you couldn't move your camera which was shit. I re-apply the downed animation every few seconds if it somehow gets cleared but it's not easy to get right, especially when dealing with lag/desync.