Inconsistency shape display (Anti-aliasing)

I created a shape of two horizantal lines. They’re not displayed the same way when I change the Zoom level of Diagram.

Enlarged image :

Code here

Is it possible to avoid this problem ?.

As long as there is anti-aliasing and one allows zooming, no.

Say those two horizontal lines are 20 pixels apart. At a scale of 1.0, the lines might be drawn without any anti-aliased pixels. But then if the scale changes to be anything greater than 1.0, there has to be some pixels that are not fully filled. And depending on how the lines are positioned, the lines could each well have to be drawn in two rows.