The Keystone of The Oblivion at no point in the description or the wiki says that when you right click it over another item in your inventory, that item will be deleted. Also, it shouldn't be able to delete items with a lot of data in them like Backpacks or Bundles.

I had found the item in a chest and did the typical action of placing it into a Sophisticated backpack by hovering the item over my backpack in my inventory and right clicking. This deleted my backpack. The item does not say it does that. The wiki does not say it does that. I imagine this can easily happen if you tried to swap items in your inventory with it, only to lose something important like a dragon egg or a beacon. While I'm fairly sure there wasn't anything beyond a lot of random nether loot in that backpack, it feels extremely unfair to lose all those items from a feature that isn't even stated on the item itself.

There should at least be some kind of indication it does this or a way to retrieve the item if this happened.

the exact same thing happened to me and unfortunately i had a bunch of important itens :( if this could be solved, it'd be awesome

I also met this issue. Right click the backpack with an item typically means to put the item in, and this operation conflicted with the oblivion stone's deletion action. I lost 2 backpacks :(
Maybe setting the item disabled by default is better.