Both of the weapons have a tendency to not return properly. I think it's just slow to return sometimes, because this problem is reduced a lot if you just wait a bit.
However this problem compounds if you are using both later on. For example, the Nyrulna explosion will friendly fire. So waiting for the fist to turn into a weapon is not a good judge; you have to check inventory or scan the battlefield.
Leaving one of the weapons on the battlefield at some point and only finding out later is a painful experience. I have used them in 2 games, and in both I only ended up with one of them because I had no idea where they might be.
Suggestion: Have those two weapons return to the thrower at combat end so they don't get left somewhere.