Old bug, has remained since tech test. Would make me happy to see this fixed. Appears to happen when landing on any sort of uneven ground. Even happens on flat ground if you're at 1000 altitude.
I get the slope thing, your immunity goes away as you tuch ground, but then you slide down the slope and it kills you. only way to fix this would be to give players some sort of immunity to damage for x amounts of seconds after touching ground i guess
