It seems that there has been a confusion here. The Scroll of Treasure is NOT related to Even More Gullible's Travels.
Scroll of treasure is the reward from the San d'Orian quest To Cure a Cough. Here is the information given by the key item :
West is a gate,
North lies a stream.
Stand on the spot
To see what I mean.
This information indicates the signpost found at H-6 in East Ronfaure, where you can obtain 3,000 gils, the true reward for the quest.
I still don't know why the "temporary" key item doesn't disappear once I obtained the money though. ^^