I have a plot that is constituted by 3 plots together (using subplot). Each graph is composed of several lines, in the positive and negative range (between y=-1 and y=1), but all of them have some region that y=0 (at the same time).
In this y=0 region, instead of having a plot of one thin line, my line is sometimes thick, as if i have used plot(a,b,'k','linewidth',2), but i have not done it.
When you zoom in the effect disappear. If you change the size of the window, it can vanish or appear in other region.
My real problem is that it keep there when export to EPS, specially if i try to make it smaller.