My thought would be this is just a graphics glitch. When you exit the sketch, does it dissapear? If it only appears while sketching, I wouldn't worry about it.
Yes correct ,Thanks Mr.mark
I too have noticed these zig zag line, never had these until started using 2012.
I just zoom in and out and they seem to disappear.
Could be a graphics card issue but not really a major issue for me.
Mark (SolidWorks 2012 sp4)