Quoted from Drewblood419:Something similar happened on my friends whirlwind and it was a form of flasher ghosting
This is a known problem on System 11 games due to the flasher circuit sharing the same circuit as the coils, with the workaround being to add diodes to certain coils.
On WPC games, the flasher circuit runs independently from the coil drivers, which is why this is a mysterious problem.