User blog comment:Rassilon of Old/Young Justice spoilers at Comic-Con 2012/@comment-188.60.137.84-20120813182357/@comment-5145408-20120814023157

While I have no evidence to support this, I highly suspect that the glamour charm wasn't specified to Wally, Aqualad, and Nightwing, but instead, anyone who was there when it was put on could see the real her rather than than the illusion.

Because, as you said, if the charm was specific to Wally, Aqualad, and Nightwing, than, yeah, that is getting way too specific and would raise some questions unless Nightwing really does have his way with Zatanna to the point where she would ask zero questions. ;)