"I wish," said Karyn, "that me and Jon can't be affected by Sarah's magic against our will in any way, including changing of our memories, and that we'd always know what magic Sarah uses against us." Then she handed the stone to Jon.
For the rest of the day, they were very careful with their wishes. It wouldn't do to create another Meg-style disaster; the biggest thing they used the stone for was to wish up a movie instead of renting it.
But the next day, they encountered the first instance of Sarah using magic that they were aware of. It wasn't an instant change like the stone. Instead, they saw that slowly....
