hmm, I understand what you mean and agree, but even so, this can be solved.
In that case, while he is in the Woods, while you don't need to protect him (respectively when you need to complete first and fouth objectives of this quest), you can make him interact with you, by showing to you the same three options to select (like when he is in his shop). Making him a movable shopkeeper.
The Buy/Sell options are obvious, but the Talk option, would be to continue with the quest (first when you meet him and the second time on the beginning of second screen).
while his quest(or future quests) is active, only his location changes, you can always make Remedi leave behind (on his shop door or even inside it) a warning signal that say where he is. if, in the future, you intend to make him go investigate other places to create new potions again this is a good overcome to the problem and you continue to make your point a valid one.
The Shop would be only his main place to be found, while not in a quest to investigate new potions.
Note: this now seems like a suggestion then a bug lol
anyway I understood your point as well, this is just a sugestion to improve in future versions, you don't need to follow it, if you don't want to.