Wow, that is an oddball one! It's funny when you track these oddities down how they can sometimes be worked out. Have a SWE1 from a mate for a few weeks. Did some shopping, repaired the pop-up targets (one not working, seemed the steel switch handle had fallen off). Changed 38 lamps (!), rebuilt the flippers - and then found I had a ball trough issue. Worked through the schematics (and a healthy dose of nuggy telephone tech support) and tracked it back to that switch that I'd repaired - and noticed **why** they'd apparently removed the lever to stop it activating - the bloody positive wire was soldered to the wrong side! Whoever had attempted to repair that switch (it was clear the diode had been changed, probably to try and solve the same issue) had soldered the switch in wrong, and knew enough to disable it as the cause, but not to see that the thing was obviously wired incorrectly.
Sorry to hijack! Let us know if you work out the *why* this was done, I'm interested to know.
