I have told darwood and uksnipperman about this bug.
If you go into the buy menu, and then are killed. If you quickly buy a vehicle ( I was trying to buy a k22 ) you can sometimes use the vehicle until it is destroyed, at which point you are still alive and can survive anything. You can also teleport and use vehicle based weapons, but you can't use you own weapons.
You remain " undead" until you relog. You cannot move out of a vehicle. But you can drive vehicles. If you want further discussion I am available tomorrow