Sounds like a correction layer.  I wouldn't say 
it's common, but it does happen whenever the 
artists thinks the lines need a little touch-up 
before going under the camera.  I have a few 
myself.

As for the correction layer not sticking to the 
cel layer, you shouldn't have anything to worry 
about.  Layers stick because of paint adhering to 
the back of the cel it's painted on and the front 
of the cel that is behind it.  Your Kurama cel 
shouldn't have any paint on its front and the 
correction layer shouldn't have any paint behind 
it.  Paint-free zone=no sticking.  ;-)

JP