Lava is meant to be avoidable, by skipping (running and jumping) you can kind of get over it and lose little or no health, I dont see why we should change this, it's already set into the minds of mappers creating climbing maps.. (if you catch on fire inevitably when skipping it might make some climb maps impossible to complete, not that it will matter much, just be a pain in the arse)
oh and the FPS lag is fixed next version (like iDante said)