By any chance have you binned the 8300 sensor?
Looks like blooming due to the horizontal shift register. I am only asking this because I have seen this on bright stars when binning 2x2 with my own sensor.
This is an example quite close to what I experienced:
http://www.pbase.com/wjshaheen/image/134819312/original
http://m2.i.pbase.com/g4/02/508502/2...2.UDJWqM9M.jpg