I have used the sweep pano function on various NEX bodies like my NEX 3 and 5n and also on the RX100. I am wondering why this is occuring on my NEX7, its unusable, and I have never really ever had a problem with sweep pano on a Sony before the 7. No polarizer, every shot has this issue.
I got this issue when I would "slide" the camera through the air. The advice I got was to rotate it about an axis instead, and that seems to have stopped it. Sliding it sideways causes a parallax error which leads to the banding.
