When I first tried creating zoom-out maps with x and y using different scales, one of the tiles for a line across the map disappeared when the game was run. When I changed to x and y scale values that were equal, all the lines were shown.
  Now, while watching a screen video rendering process using CamStudio, I am seeing the same line disappear and any tiles on layers above it on the line but the final video rendering is o.k. Can anyone explain what I am seeing and why the line disappears?
  

Can you provide an example?

Is this on 1.5 or 1.6?

It's version 1.5. I am searching for some screenshots I took but I may have deleted them. It looks like a tile with a line that is tiled across the map near the middle of the screen is missing. Yet, the same map tile is working fine for lines running across the top and bottom of the map.