There WAS a bug that made you speed up as you moved across rivers, but crushing that may have adversely affected the movement along them. Ilteroi has been paged.
Okay, let's just get technical, how many movementpoints is it supposed to take to move one tile along a river for a normal warrior? Because even before this bug-fix it always used to cost 1 point. And before the bug-fix, moving across the river used to cost 0.97 or something along those lines, so you could move 3 tiles with a warrior if you crossed a river with at least one of those tiles.