If you're fighting Bangaa or Seeq's, they will also steal your loot occasionally, but the only creatures I've fought that ever actually went out of their way to get the loot first were the Baknamy... thieving little monkeys. As well, I'm not sure, but I think that all of these creatures can only steal loot dropped by their own class... meaning if you kill one of those horse things in the Nabreus Deadlands, I don't think a Baknamy can come along and steal the loot for that. I might be wrong though, it's just never happened to me.
He who fights with monsters might take care lest he thereby become a monster. For when you gaze for long into the abyss, the abyss gazes also into you.