Saw this too today.. What is pixel alignment? My pixel layers go way beyond the artboard boundaries, and yet when I switch to pixel preview, the left and right margins look pixelated (extending outside artboard 1 pixel.. what??)
Do I need to have that on when I create the new artboards? As after reading this comment, I turned it on, made a new AB, copy pasted the info from the other AB, and it looks ok..
However even after turning it on, and working in the "old" artboard, I still got the line, even after deleting the content of the AB and pasting content from the one with PA ON. I know this is the bugs section, but if the problem is already being discussed I might as well just ask.