That maple leaf batch I tried last fall made the paper way too brittle. The pieces kept cracking along the veins when I tried to fold it. Natural stuff just doesn't bind the same way pulp does for real use.
Yeah, the trick is blending the leaves into a pulp first, not just sticking whole ones in. Tear them up, soak them overnight, then beat the heck out of them with a blender. Mix that mush with your regular paper pulp, maybe add a little extra binder like cornstarch paste. Lets the leaf fibers actually bond instead of just sitting there waiting to crack.