I can understand playing devil's advocate, but as you said all that's needed to make this magic item is to cast the spell, then that's not enough to make it a magic item and not a spell effect. If I cast invisibility on a ring, do I have a ring of invisibilty? No, I have an invisible ring. Now, if I used the craft ring feat and spent the gold and XP to make the ring susceptible to magic, casting invisibility into it suddenly makes it a ring of invisibility.
Isn't it more logical to assume that a human being made a mistake and put it into the magic item section instead of in with some of the other special items, than this is a magic item unlike all others, when any spellcaster can make one just by casting continual flame on a stick?
Playing devil's advocate is fine, but once there is overwhelming evidence/opinion that your position is wrong then it should stop.
IceBear