I'm able to start surfing on still water (Terrain tag 6), unless I'm facing up.
The red arrows are the side I can't surf onto the water from. Any other side works fine.
I've looked at the example maps, and I still can't figure out why I can't surf on this map, but I can in the examples. I'm using the same tileset as the example maps. To be specific, I'm using Route 2 as comparison.