Its not the items it eats, its the weave itself, the magic itself.
So,... well, the excuse could be if it eats away the magic that is used to change the tadpoles, the tadpoles would assume their normal functions or do it suddenly all at once, so that would not be a good thing to do. Still... one wonders how exactly that magic devouring orb doesnt devour any magic that comes close to it, including the one around or inside the tadpole.
That is a very interesting argument.
