I was about to make a blog entry on how tracing an analog pin (in this case from an Arduino 2560 Mega) can add noise to the digital lines. Then I realized what digital line I was looking at. This is D1 (the transmit - TX on the board) . So, I was looking at the Analog trace data being transmitted on pin 1 back to the computer. If you think about it, both the analog trace & the digital trace have to be transmitted back to the computer. So this D1 info at the top of the screen-shot is some of that data. And the trace at top is of itself working correctly.
Just one of those, Ah-ha moments :)