It's been a while since I've actually fired up the game, so I don't know if this is new or not, but I noticed one of my soldiers was accidentally hit by a flamethrower blast which didn't do anything to that soldier. As an experiment (I was testing in skirmish mode) I fired a full "inferno" at one soldier with no armor, and it didn't do any damage at all.
To compare, I also had a few soldiers blast each other with shotguns and rifles, those all worked fine, with expected results.
I only had this happen in one mission, a skirmish, I'll try to see if I can reproduce it.
Edit: A quick search in the bugtracker didn't reveal anything previously reported regarding this issue. If I do find I can reproduce it I'll open a bug report.