Well, to some extent I can see your problem. Indeed there seem to be no slots in the 'MOP:FUNCALLABLE-STANDARD-OBJECT class. The layoutFuncallableStandardClass is what confused me, but that's indeed the layout of the metaclass.

So, you're correct that the fix works by accident. The solution should be to add a slot by the name 'MOP::NAME to the FUNCALLABLE-STANDARD-OBJECT. That slot can contain the name of the object (ie function) for which the item is defined. In that case, we should probably remove the direct slot MOP::NAME on the standard generic function, since it's already defined on the superclass if we decide to do that.