If your GK64 is like mine, PCB mount switches (with the 2 extra plastic pins on the bottom) don’t quite fit right. They start to go in, and go in most of the way, the pins make contact, and the switch works… But if you look closely you can see that the switch didn’t snap all the way into place. The right-hand side of the switch won’t go in all the way.
This gallery shows why, and how you can fix it.
dl;dr - Drill it out