Very strange, as mine started exhibiting the exact same issue this afternoon. I also have an Opus 120. The first time I noticed it was when I shut the car off and went to the bookstore. When I came out, I started the car again, but forgot to enable my killswitch, so the machine resumed from standby as it should, but I only drove it to the other end of the shopping center and then shut the car off again to go to the grocery store, so the car was only running for about 2 minutes. When I got out of the grocery store, the machine started up as though from a cold start, and not resuming from standby. When it did so, my GPS was messed up, and it took connecting a mouse and fiddling with XPORT for a few minutes before it came back up. I then drove it for about half an hour, pulled it into the garage, shut the car off, and opened the trunk to remove the software CD I had inserted in the machine, but the system was already shut down, so it's happened twice now on the same day. My OPUS120 is set up by jumper to standby after 10 minutes. Today was the first time in the 5 weeks I've had the system running where I had any kind of problem.
I'll have to do some more detailed testing this weekend. I've got a distribution block in the trunk with an onboard voltmeter, so I'll see if the battery is dropping too far below 12v when I turn the car off. Maybe that is causing the system to shut off. However, I kind of doubt it's a voltage issue because the system restarts cleanly. It doesn't go through the windows checkdisk function as it would after a power loss.
The only other thing I can figure is maybe heat, but then again it would run checkdisk if heat is killing power to the system.
It seems to me that maybe it's something with the OPUS120, shutting the system down instead of going to standby. I'll have to see if the jumper maybe worked itself loose or something.
I'd hate to have to RMA the OPUS.