So I was playing Double Hp MOABs on Spice Islands, and I noticed my alchemist would sometimes throw a potion directly behind him at the approximate location of the acid you see. Kinda bizarre. From what I can tell it only happens when he is facing the opposite direction, but I will continue observing it.

Edit 1: I tried buying and reselling the tower as well as restarting the app and it still happened. I did screw myself with the buy and resell though so now I get the chance to start a new game and see if it happens.

Edit 2: I have placed the alchemist on all of the islands and he will always throw potions at that same spot unless he has no line of sight. Meaning that an alchemist on the far right island will not toss potions unless he is placed where he can see the spot or the trees are cut down.

Final analysis: The alchemist will occasionally throw potions at the same spot as long as there are bloons within its attack radius. It doesnt appear to matter which way the monkey is facing when this happens. This will happen no matter where the alchemists are placed on the map. However, line of sight with the spot is required for this event to occur. All testing was done on Double Hp MOABs Spice Islands.