And I'm not really sure how or why. I've finally gotten pretty good at controlling myself when it comes to hauling around crap I kept telling myself I would eventually use for weeks at a time (once Dragonborn was installed, Apocrypha become my own personal hell), so I'm used to seeing my carry weight being at a comfortable 250-400 pounds, or whatever unit it uses. I noticed earlier today though, while I was looting a Dwarven Centurion Master, that it seemed awfully high, indicating that I was carrying almost 680 lbs worth of stuff, and I don't recall picking up anything real heavy recently.

So I did the calculations of everything in my inventory (that didn't weigh 0) and sure enough, by my calculator, it came out to an even 290 lbs. Where on earth did those extra four hundred pounds come from? Any idea what might be causing it?

I often carry a lot of potions and soul gems and often forget about them. The weight adds up. Also, I do recall that increasing weight got glitchy in Oblivion when it went over a certain amount. Wouldn't be surprised if the bug carried over.

Yeah, I recently dropped off a buttload of potions and soul gems and ingredients in one of my homes, but it's still in the high 600s, and like I said, I calculated everything and it doesn't add up. :/

You have any quest items in your inventory? Sometimes the devs forget to make them weightless. If not, It's likely the bug carried over.