ok, interesting, and I think that's a good change actually. In the first case, you're not using your mental power so much as channeling an item... in the second, well, it's nice to have some niche cases where you CAN cast two levelled spells.
EDIT: SORRY, I see this was already discussed. Seems like replies are not nested under original comment, which confused me!
Quick point. As I understand, the DM was wrong... you can cast one level spell on your turn, but more than one in the course of a round. A reaction takes place on another...