I did a couple more tests.
I took off J12 from the ignition and manually connected it to +ve (same as J11 but through another point). The PC boots at this point.
Once the PC has finished booting up and is showing the front end, I disconnected J12 from +ve and in 10 secs the PC goes into standby mode.
All is fine.
But now, I connect J12 to +ve again, and the PC goes hard off for 1 sec and turns on again. So now I've confirmed its not car electronics but its the M1-ATX itself.
Does J12 need amps as well or does it just monitor the voltage (12V on J12 sends J6=0V and 0V on J12 sends J6=infinite)?
The second test I did was, after the PC goes into standby mode, I manually short J8, and the PC boots on and resumes from standby. Then I put the key in the ignition, turn it on and the PC shuts down, and reboots again.
Almost 20 people read this, is it me alone that experiences this problem with the M1-ATX?