Erm...I don't mean to judge, but the mortem can be put in the mortem tags (look for the button with the DoomRL logo) and pasted directly into the post. No need to .rar it.
I've heard of other people mentioning that planeshift boots can produce the hovering quality that should occur work when both pieces are on, which continued to persist without the boots. If there's anything else you can mention (what other equipment you happened to be wearing, any mods, were you knocked into the lava at any point) that wouldn't be listed in the mortem, I'd do that as well.
As a counterargument, I managed to find planeshift boots in a standard HMP run today but still took normal floor damage while walking across lava: I just hope it's not at random.