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 :)