If you cast Fury on an enemy when they've got their weapon drawn, they'll resheathe it when the spell hits them. The time it takes your enemy to unsheathe its weapon is long enough that you can get an extra, unblockable, unavoidable attack in.

Would you consider this an exploit or is that just how the spell's supposed to work?

sploit

Yeah, but see, I'm asking because I imagine if I were suddenly enraged, I'd have a moment of confusion and nonplussed-ness as I tried to figure out where to direct it. So ...

Then you already have your answer.

If I were suddenly enraged I dont think Id sheath my weapon.