Horizontal line, close to header part line, is invisible, drops into another dimension (I guess).
In 13.0v2 - I have a layout in list format. I want to have a horizontal line along the top of each record. This is a 1 pica black line, set to be perfectly horizontal. If I position the line just below the header part line, it disappears! If I move it up by one pica, it appears in the header. If, alternatively, I move it down by one pica instead, it appears in the body part, but with a thin white space above it, between it and the header part, such that it intersects the tops of the fields I have positioned in the body part.
Ah. Answered my own question. My line was one pixel higher at the right hand end than it was at the left hand end. So it wasn't perfectly horizontal after all! This was devilishly hard to see. At 100%, I didn't notice the discrepancy. When I went to 400%, I saw only a small segment of the line, at the left hand end, and missed the fact that it was, in fact, slightly slanted. I have no idea how it got that way, because I always hold down shift when changing its length, to keep it at 90 degrees. But if it's already at an angle, this technique does not fix it. When I went in and adjusted it, manually, the problem went away.