When the "Advance right bonus" 500 switch (mid-way up the right playfield, just under the "Scores right bonus" eject hole) is hit, the right bonus ladder advances one position as it should. Immediately afterwards the left bonus unexpectedly advances one 5,000 point spot. Can't figure out why. When the top center 5,000 "advance left/right bonus" is hit it works properly - advancing only the left or right bonus as called for. Spinners do the same: left spinner only advances left bonus, right spinner only advances right bonus. I do have the instruction manual and schematics, but please consider me a rookie if you have suggestions. I have come a long way with this game - it would stop play after draining ball two and four (old forum posts helped), and also would not advance to the next player after player three and four drained. But this phantom bonus advance has me stumped. Thanks, Henry