This took a while to figure out. The code that cause damage to a player is actually quite complex, and at some point for "safety's sake" someone set it up to silently fail if there was no attacker doing the damage. IMHO it's better to fail loud in those cases so we can fix it.
In this case, it's environmental damage, so there's no creature to blame.
I remove the silent failure code, and uveto now does cold damage again. However, it's possible that this may expose more crashes elsewhere.