Possible bug, no movecost at sea?

[Hafting]

I make new terrain types. Right now, sea and lakes with ice floating on top. After some problems, I was adviced to implement this as new terrain types so the move cost would work.

So I made a new terrain type, "icy lake". Ice is a navigation hazard, so food & trade is lower than for a normal lake. This works, the frozen lake was less productive.

The ice should also increase the move cost, so I set "movement_cost=3" instead of the normal "1". Comments in terrain.ruleset indicates that this is the way to make a tile slower.

Started a game, used edit mode to place a trireme. I expected it to spend its 3 move points on a single tile move in the ice, but it moved 3 steps as usual. The same with other ships - they move through icy lakes just as fast as they move through other lakes or sea.

Am I misunderstanding something, doesn't movement_cost do what I expect? Is there something else I must do? Or some sort of bug?

[cazfi]

Likely sea units class does not have "TerrainSpeed" flag, and thus those units always move like the movement cost would be 1 (like air units flying over the terrain).