That looks like the stock makers nightmare an internal stock blank crack. This sort of problem could be hidden by a craft stock maker because he would have sufficient matching wood he had removed during the basic shaping to patch it. Like a lot of production today the use of duplicators for producing the stocks basic shape with wood removed that is a little better than sawdust so no chance of a good patch repair. It looks like the crack has been filled with an epoxy filler and leveled down before it was truly hard, Oh! the benefits of mass production and poor quality control, and a machine minder's ham fisted attempt to make things better.
