I thought if you dc'd during crafting it acted as if you never pressed any buttons, so I figured it would auto-complete if you dc at the end. I know if I let the time run out on a finished item normally it still completes.

Is it the first time you've dc'd while finishing an item? If it isn't and the other recipes you've dc'd on auto completed, I'd imagine its due to the timing of your dc, like you left the server before the timer ran out.