Description of Bug: If you have an empty bag, and a bag with items in your inventory, it can become undroppable until you log out and log back in.
Reproduction Steps:

1.  Have a bag (I was using leaf bags) in your inventory. One with items, one empty. They should be in a stack
2.  Open the bag, the one with items inside will display.
3.  With the bag's interface open, drop one bag.
4. The bag in your inventory cannot be opened, or dropped until a log out.

Error message (if applicable):
Screenshots:

Yes this has been an issue, AFAICT it happens because when a bag becomes empty it will often stack onto a non-empty bag which I believe shouldn't be the case. Once it stacks the empty bag is essentially imposible to interact with untill a relog.

It doesn't appear to be the case. If an empty bag stacks with a full bag you can open the inventory of the full bag, but then if you drop one bag, you can no longer interact with the bag in your inventory until a relog.

EDIT:

I was mistaken, you're right. Opening and closing inventory screen fixes this.