That is usually caused by adding moisture to an already dry stave and sealing the back(snake skin)but usually with sinew backed bows. I have a halibut skin covered sinew backed bow, supposedly made by Jay Massey, that has deep belly cracks. I remember an article by Jay about this reaction. It shouldn't effect the performance as long as the cracks stay in the limb. If it doesn't already have super glue in the cracks like Eric mentioned , I would add some for insurance. Pat