I think you're talking about a character from the 1-VaultDwellerzPack modlet. Either that or you're playing the Wasteland mod, since I believe it uses that modlet. So the appropriate place to ask is in either the NPC Core thread or the Wasteland thread.
However - I'm pretty sure I know the cause. If the entity has a "LootListAlive" property, then it will show the "Press <E>..." prompt when it's dead. You could remove that property, but that would disable the character's inventory if it's a hired NPC. The NPC Core folks get around this by having hirable NPCs despawn almost immediately after they die, so most players can't get the prompt.
So either you have power armor NPCs that can't be interacted with or hired, or you live with that bug. Personally I think that bug is a small price to pay.