I thought items don't disappear when dropped. I put a recharger rifle on the floor next to a dumpster in novac and it went missing. So is it now unsafe to drop items?

Okay well now I dropped some dog hides, ruined books and various other items on the ground. They eventually disappeared over time.

So is it no longer safe to drop items? Is this outside only or inside too? Will my items in the motel room in novac disappear too?