Platform: Windows
ISP: Spectrum
Type of Internet Connection: Wireless
Internet Connection Speed: 100Mbps
Date & Time: Jan. 3, 2018 22:00 PST
Frequency: Once (did not reproduce)
Character Name: Cheezeman
Race: HumeM
World: Asura
Main Job: Blue Mage, Lv.99
Support Job: Dancer
Area and Coordinates: Northern San d'Oria - D-9
Party or Solo: Solo
NPC Name: Excenmille
Monster Name: N/A

I accepted the Ballista License Quest linked above in San d'Oria, then changed alliances to Windurst and accepted the quest again from their respective NPC. As a result I received duplicates of the two Temporary Key Items (letters) used in the quest.
When I completed the quest while allied with Windurst, the remaining Temporary Key Items were no longer deliverable and are now permanently stuck in my inventory. They are entitled "Letter to the Bas. Conflict Cmd." and "Letter to the Win. Conflict Cmd."
All I ask is for these two Temporary Key Items to be removed from my inventory, as there is no longer an in-game method to do so (I tried changing my alliance back to San d'Oria and the quest NPC's will not accept the letters).