Xpantastic!

It sounds as if the front panel is slightly out of line with its switch 
holes. Just loosen all the panel mounting nuts on the inside, just 
enough to allow a little free movement of the pcb, and shuffle the board 
around gently until all the buttons are free switching. Then finger 
tighten a couple of the nuts to hold it in place. Recheck again and if 
all it good, tighten them all up again. Recheck again and repeat if not 
successful.