Weird problem in ortho mode

I drew lines using Line in ortho mode.

When I turn on antialiasing in my graphics card, many of the lines disappear.
Some lines are still there but are located in different places.

Do you not recomment drawing grid lines in Ortho mode?

I looked at it once again.

Their positions are the same all right. Sorry.

It is just some lines' colors become washed out.

Problem solved.

I just set line width to be 1.5.

The way anti-aliasing works is to blur the rapid changes in 'slope' to give less jagged, computerized look.  I suppose when you turned on AA it caused some of the 1px lines to blur to nothing.