I tested that in a fresh copy of pokemon essentials v17, it works fine but for example: When surfing on this tilesets it works fine until a small island, but if you try to surf backwards it bugs the player and he still surfing everywhere. I'm not sure if i explained right. See the pic.
If the player wants to go right while surfing, against the flow, the char goes left because of the currents, he dismounts surfing sprite but he continuous surfing on that small island without any terrain tags. But, under sea currents tags are the surfing tags.
Like you see on this image, i cloned a map from pokemon emerald sea currents maps.
So, how can i fixe this bug? Credits will be given.