That two step motion is actually normal, because advancing it is a two step process. First the top horizontal lever comes down ( to keep it from springing back). This causes the cam to move slightly until the lever catches a tooth. Then the side vertical lever engages the cam as the horizontal lever lifts back up. This causes the second movement as a cam tooth catches on this vertical lever.

If the levers would land precisely at the edge of a tooth and have almost no movement, it would look like one step. but it would have very little margin for error.