"I wish everyone's memories, excluding mine, would change to fit the new reality." Jon waited for the stone to glow, but it didn't. "What the hell? Why didn't it work?" He paused for a moment, then said "I wish I knew why my last wish didn't work." This time the stone did glow, but the answer he got wasn't a good one. The memory wish didn't work because this wasn't his wishing stone. It was The Obvious Stone, a specific type of wishing stone that worked just like the stone he inherited from his grandfather, except that everyone would always notice the changes in reality, no matter if they heard the wish or not. His wish didn't work because it was a contradiction to the function of the stone. People couldn't both have their memories changed and remember the previous reality at the same time.
Jon dropped onto his bed, realizing the ramifications of his original wish. Everyone around town was different now and they were all noticing it. And there was nothing he could do to fix it. Thank god he had enough foresight to put a time limit on it. But this was going to be one really long day.