Ah, OK, thanks for that! I was just reading things wrong, my apologies.
Yes, that makes perfect sense; you don't have a floating circuit that way.
Well, that'll be it in practice, too, I would think. It'll just work.
I guess similar idea could be used to stop oscillations as well, such as when you have a sling with the switch contacts too close, and the vibration from the sling firing causing the next switch closure. You could count how many times in the last n seconds each switch has triggered. (Just keep a counter for each switch in an array.) Then scan the array every five seconds or so from a timer task and check whether there is an unreasonable count on any of them. You'd have to tune this a bit, to deal with multi-balls where a lot of stuff can happen in a short time. But it should effectively stop this kind of thing, especially for slings and pop bumpers.
Michi.