I've been online for less than an hour this morning and, in that time, two different items (at different times) that I had locked somehow unlocked themselves and were in the regular section of my inventory.

did you have two or more of that item? If you have one item locked, and used another item of the same name, you'll end up using the one you had first. That's happened to me.

Yes, I did. That must be what happened. Thanks for letting me know!