Have any good pics of the connector and board where you were tinkering?
That J10 connector, even if everything on it was shorted together, should only make all 4 of those back buttons press at the same time, so there could still be a short there as it doesn't take much at all to cause one sometimes. Then sometimes it doesn't even have to be a short for a button to register as pressed.
Thanks for the offer, but I prefer the controllers I use for board scans and such here to be pretty much straight out of the box, that way nothing is missing and I know exactly who's dik fingers have been on it, no offense intended at all. Pretty much every one I've done here was brand new and never saw a minute of actual game time as they come apart for the scans and then go into the 'collection' box for tinkering on later and digging out to figure out this or that issues that others have.