This shot was taken moments later and the trailing tail lights are clearly visible in this shot; and I did not change the camera / flash settings at all. The metadata shows the flash firing in both images; so all I can thing is that it was some kind of a camera glitch. It's the only image of the set where this seems to have occurred; the rest are "as expected".
The reason I suspect the pre-flash is that the car passengers are quite clear and with two equal flashes, I would have expected to see some sort of clear artifact; which I don't see.
As for the spell checker, I suspect that is part of your browser setup. I know I have it in mine (Firefox), but haven't found where to turn it off or on in the settings