Yeah -its normal...the leaves control the motion the way arms would on a coil sprung rig.

Coils only control up/down motion, so additional control points, such as arms, connect to control lateral and fore/aft movement, are required.

If you think about it...the leaves are connected infront of, and behind the axle, and, control fore/aft motion as arms would, as the leaves are essentially arms in that context.

The leaves are flat plates that resist lateral motion, allowing up/down, but inhibiting side to side motion, as a triangulated rear linkage would, and essentially function as an arm in that regard as well.

Think of the leaves as springy arms, and it might make sense.