I did some more extensive debugging tonight. I logged every property of every event that gets reported to Double Duty and, sure enough, there are “phantom” events that get sent from certain devices that are completely indistinguishable from the real event. They do get reported as a separate event though, so I can’t even do something like log the event ID and ignore duplicates 
It’s really a shame because I feel like this is such a simple but handy application. I am still using it at my house, but my recommendation is that you use only either on or off presses on a particular master switch, not both. At least if you leave one of the two “dead” then you have ways to offset these events. For example, my track lights “on” redundant press toggles a corner lamp. If I turn the track lights from off to on and it sends a phantom event causing the corner lamp to also turn on, no big deal I just use another redundant press to turn it off. Or, if I want to keep it on but the track lights off, I can then turn the track lights off safely since I have no behavior attached to “off” presses.
tl;dr: There’s nothing that I can do to make this app work better, it is written correctly. This is a device/platform limitation/bug causing this. If you continue to use this app I would recommend only assigning behavior to either “on” or “off” on a master switch, but not both. This way you always have recourse to “correct” any odd behavior 
… that wasn’t a very good tl;dr!