I built a take-down longbow from binghams. It has a bubinga riser and the limbs are maple with black fiberglass. It turned out nice and has been shot probably 500-750 times with no problems. It turned out about 35-40 lbs. I noticed that the limb glass is splitting where it attaches to the riser, about 4 inches long, between the limb mounting holes exactley the same on both limbs. What could be causing this?