You see, before patch 1.49 (or was it 1.47?), items that you have equipped were landing on the slot in your equipement, and the item that was there before was moved to the slot where the item you used was. However past this patch, no matter where your item that you want to use is, the unequipped item will land in the first available slot in inventory, looking from top left corner, as if it was newly obtained drop.
Now perhaps is your first, default inventory is full and item is supposed to land on your other bags, the bug might appear. This is just a guess though, but i haven't encountered this bug and i always clear my top slots for the drops, so i can see them right away. Auto sorting button is not helping with this. I really hate that button because if i click it, it moves all items from top to bottom and again i need to clear top slots manually.
Before you quit, try to do the following:
1. Check out if your ring slot in equipement doesnt have it hidden on different build for some reason (click that arrow to see if its not there maybe).
2. Try to move items in inventory to different, empty slots - perhaps its just invisible, such bug was happening before too.
3. Use sort button and try point 2. again.
4. Make trade with an alt account and try to reach the point of your inventory being full, and thus not allowing trade. Count the empty cells before you do that and count the number of slots the items traded to you will take. If you will have 1 empty slot left but you wont be able to trade in another item, chances are, your ring is still there, just invisible like i said.
I really don't know how to help you more, but this is what i would do if it would happen to me.
Nowadays before i unequip/equip something i am making screenshot of my inventory, just to be sure to be able to provide both before and after screenshots for the report.