Title is self-explanatory. I tried mounted and dismounted and it didn't make a difference.
Did it spawn a new agent (horse or actual player)?
Also was this an actual medic station or a pot of stew/beer?
No new agent spawned.
It was a cask. I guess it's not supposed to work on those, since I tried it in Ragnarok just now.
Yeah they only work on actual medic stations ;)
All right, closing, but why the distinction?
A small bit of realism. If you look at the medic stations you can see all kind of surgical tools needed to perform these kind of operations.
While it is debatable whether beer kegs could have the same effect, since the influence of alcohol will temporary sedate you, so you can remove the projectiles, I think it is best to limit it to the medic station.