Easily reproducable bug. Many times has it allowed me to move freely around the edge of the map as if it wasn't difficult terrain. It says difficult when right-clicked though. And sometimes it counts as a difficult terrain, for some reason. Hovering mouse cursor over the move card shows correctly how far you can move with it. Once today it showed me correctly only 1 square in both directions. Then we passed and at the beginning of the next round it showed full 4 squares in both directions over the water.
Ah, no, I'm just dumb. There has been a way to get to these tiles around the blocked terrain in the middle and not through the difficult terrain -.- Chess madness is maddening. My mistake :S :S