Buggy Grenades?

[jamz]

Absolutely to do with your ping. Nades often go in different directions for different players/the server, because the clients have players in different positions at different times. Usually you can cope with the effects. These are extreme examples and there's no point trying to counter it.
I assume from your reaction that you saw the nade go down to the armour when it happened? I would have expected the demo to show it bouncing back on you but...well...