Remove Materia and add back in?

[Kenyon]

I removed Craftsman's Cunning III and IV in the second and third spot from my Chrondite Cross Pein Hammer leaving just the first slot with materia. When I went to meld something else in those slots the message I get is 'You cannot affix any more materia to this item' Why? I tried melding the original Craftstman's Cunning back in and got the same message. So I cannot even restore the item to pre-removal. Why is that?

Edit: I removed the Cross Pein Hammer, added an old item, did a few melds, then put the Cross Pein Hammer back on and now I can meld it. What???