Debounce does not affect the probe input, if using the parallel port.
For the 3rd time, are you using a parallel port or motion controller?
When other pins are being triggered and the X axis is moving because of the probe input, then I don't think it's the probe wire itself, but rather the probe wire is creating a ground loop somewhere else that's wreaking havoc with your system. It would appear that this is freezing Mach3.
I don't understand why the probe works if I hold the plate in my hand and touch the bit, but not if I put the plate down and let the bit touch the probe plate.
Once you set the plate on the machine, it's causing a ground loop to be created. The fact that your X axis is moving means that it's very bad. Are you using shielded wire for anything? Are you using Star grounding? You may have multiple problem areas and the probe is just part of the issue.
When the probing stops at the plate, and won't move, is there a message displayed in the status bar? There should be some probing messages. What's the last one displayed?
Also, if the probing macro (or any other macro) does not finish, you MUST restart Mach3, or you could get strange results moving forward.