Beaky is 100% correct about the poor design....what were they thinking? I come across this type of thing a lot when I am redesigning boards - all I can surmise is that they threw these machines (all brands) together at such a furious pace nobody was too bothered about getting small details right - if it worked, that was good enough!
In any case - after you sort out the issue - I would strongly recommend adding a resistor from the point marked "pin 1" on the left side of R41 to ground - probably about an 82K should be low enough in value to hold the output FET (Q3) OFF should the wire or connectors have an intermittant issue in the future and high enough to prevent interfering with normal operation.
