
What I did: after my run, I had 4 items in my backpack. I took one of them (the Crumbling Ward) and lockered it. Then the 4th backpack item slot disappeared visually, however hovering over it confirms that it's indeed considered to be one of the remaining items - the Troll Heart.
I can drag it and drop it over another slot (there is no graphics - I just see the pointer, not the item), then it asks if I want to re-locker.
If I move over to Bezaar (or go into another adventure), it shows properly in the backpack as the Troll Heart. However even after going back into the Guild screen it continues to show as an empty slot there.