I don't totally understand this, but from my understanding:

There's a difference between Selective Enrollment (gifted and classical) and the magnet schools where you are accepted by lottery.

As soon as you accept at a Selective Enrollment school, they take you out of the pool for consideration at other Selective Enrollment schools, but NOT for magnet schools.

Also, when you accept at a Magnet school, you are NOT taken out of consideration for anything, you are still under consideration for both Selective Enrollment and other magnet school's waiting lists.

Someone please correct me if I am wrong!

Eric