My guess is that it must happen some kind of accident (like something that fell and hit that button) for them to break. Maybe in the shop, or a previous owner. Or you're being too hard on it

Maybe also, a bad assemble, in which case the button must have felt funny probably from the start.
As mentioned earlier on this topic, the freezing problem is not button related. Take a look to your serial number, and if it's too early, chances are it belongs to a bad batch which needs a capacitor to be replaced.
I dare to say that Korg would fix that even out of warranty.
I must add, a couple freezing situations reported here were related to a bad relationship with some sustain pedals.
All in all, really strange that this locate button thing happened to 2 units, and the same button. The kind of thing that makes people paranoid about it.