Ok, first no I didn't deliberately check "shutdown when finished" or have it auto-checked from the settings.
I usually burn in batches, 10+ discs at a time. Occasionally I will cancel between burns, but not close the program, if I want to pause burning for a while. Twice when I have canceled between jobs I got the "save Queue List?" prompt. The first time I wasn't sure why I was getting it, but I said yes and saved the Queue to be safe. Immediately after saving the program closed and shutdown my computer. The second time this happened I clicked Cancel and was returned to the main program window as normal, then later continued burning the rest of the Queue. When it was done burning the queue I was back at the main program window and I just closed the program like normal. It then proceeded to shutdown my computer.
The last time it happened I did notice the "shutdown" checkbox was checked somehow, perhaps that box got focus when I wasn't aware and I checked it somehow, I'm not sure. I unchecked it before the job finished and continued burning the Queue.
I'm not sure if this is some kind of bug, or perhaps just a UI problem that is causing it. I will sometimes pause the burning to play a game and I'll occationally alt-tab out, which can be problematic, so perhaps that is playing into it, I don't know. I haven't tried to recreate the problem.
Luckily I haven't lost any work because of these accidental shutdowns. Regardless of the cause, I think it would be nice if the program had a countdown to shutdown with the option to abort.