[Q] Force minimize bug across multiple ROMs topic

The error is a "force minimize": the phone minimizes the currently running app and brings up the home screen without any provocation.
The app is not closed; for example, during an ongoing call, if the handset is removed from the ear so that you can key in a number, you will still be able to hear the other party and the green "call-in-progress" icon will be visible in the status bar, but the dialer itself will have been minimized.

If "vibrate on touch" is enabled, the phone vibrates whenever the minimize occurs, as if an invisible hand is pressing the home button. Sometimes, there are multiple vibrations, as if from repeated home button presses.

I first faced this issue when I dirty-flashed an April CM12.1 nightly over the CM11 20141010 snapshot. Unsatisfied, I went back to CM11, where the issue popped up again. I then switched to MaximusHD 10.0 (for which I had to flash the provided 3.4.10 firmware before installing the ROM). Again, same issue.

So I now have a phone which behaves erratically across at least three versions of Android (5.1, 4.4 and 4.2). It had been running the same ROMs earlier without any issues.

Specs:
S-OFF
HBOOT 2.16
Radio 1.20

Could someone kindly help me troubleshoot this? Could it be a hardware issue?