The flavor is meant to indicate the aura being stored in a box.

Oops! I put this in the wrong set.

Would it make zero sense to phrase Store as an action?
­: Store ~. (~ becomes a colorless artifact and loses all abilities. You pay pay to end this effect and attach ~ to target permanent.)
It would be nice to potentially have abilities that trigger "whenever you store an aura" or something.

I'm a big fan of this type of effect, though, I must admit that the times I've printed things like this and had people playtest them they always come back with questions. Whatever. Changing types is awesome. Suck it, new players.

I do think that you have to add the word "unnattach" to store, however. Not because the card doesn't work as printed... I think losing 'Enchant permanent' really does the trick. It's just... well, you're going to get questions from people who don't know that, and it's just a couple words more to stop those questions.

Also, I personally think it might be better to have "Whenever a permanent enter the battlefield, you may attach..." Instead of paying to end the effect. That's roughly what's going to happen anyhow, is simpler for some players to parse, and strangely, cuts down on decision making. You'd think it would increase it, since you'd need to make the choice every time you cast a creature... but with the mana payment, the choice now becomes "Whenever I could potentially use ."

Hmm... it would then have to become: Store (: ~ becomes a colorless artifact and loses all abilities. Unattach it. Whenever another permanent enters the battlefield, you may end this effect and attach ~ to that permanent.)

Until today, I never even noticed that cards aren't referred to by name in reminder text.