Items of dead character disappear but leaves ghost effect

Eder died and I picked up his equipment after the battle was over. I have distributed his items among the party members, and some in the stash.

After I have traveled across a couple of areas I have noticed that those items have disappeared from the equipped slots, and those from the stash as well. But their effects remained on characters that were equipped with them, under the name "[charname] Attack"

In the attached screenshot you can observe the ghost effects of a Minor Ring of Defense and a Girdle of Blunting that were equipped on a hired NPC and then vanished.