I had a player complain that the Airfield Quests delivery mission sent him to the same Airfield Quests delivery NPC.  He was unable to make the delivery to the same Quest delivery NPC. Luckily you can cancel the mission but because I'm using NPC's, they have to go out of their way to do so.

Is there was a way to prevent the delivery vendor from selecting itself as a delivery destination? 

I have 11 Quests delivery NPC set up just in case you ask.

Update in regards to delivery missions. I had more than one Airfield delivery profile after deleting the extra profiles everything was fixed. this includes the vendor as well I had one vendor called Russian and the second one called Ninja after deleting the Russian from Bender ninja worked.