Probably the shovel version. Similar to armor "Upgrading" to a higher tier (Leather to chainmail, for example) gets rid of the older armor entirely.

If you have better armor, like platemail and get leather armor, it'll go through, but the leather armor will just vanish.

Since you have literally any other better shovel, the glass shard just goes away.

I might as well just remove glass shards from the item pool, or at least that one.

It disappeared when I picked it up, I'm not sure if that changes how you interpret it.