It's a little too easy to lose unique rewards forever

[Mharr]

I just went to sell a bunch of junk weapons to a shopkeeper, not noticing that I had completed the quest stage for that NPC that gives a unique item reward (Grand Pistol). Of course I didn't have inventory space, so access to Powerful 4 on guns is dead to me now.

Could quests with item rewards maybe fail to hand in if there's not enough space? That's the usual system for preventing this sort of thing.