How do I select a line in preview

Thanks for kicking me in the right direction. I think I've found the issue: perfectly horizontal lines cannot be selected the way you describe. It appears Apple's built-in screen capture utilities either won't capture the pointer, or will fake one in, so there's no built-in way to show a screen shot, but if I could, you'd see that even when the pointer is directly over a horizontal line, it looks like the crosshair in your first screen shot.

If I show the inspector and click on the row for the horizontal line, the pointer becomes an arrow (immediately, without being over the line) and the line appears selected. But if I mouse over the line and click, the pointer immediately becomes the crosshairs again and the line loses its selected property.

Starting from scratch: If I click on the row for the horizontal line again, the pointer becomes an arrow (immediately, without being over the line) and the line appears selected. If I mouse over one of the endpoints of the line and click, I can drag the endpoint, which will make the line not horizontal. Then I can deselect the line (while still using the line pointer) and hover over the line (not the endpoints, and the pointer will change to the arrow and behave as you describe.

Well that's a pain -- selection of horizontal lines in Preview 7.0 under a different user works fine. Still doesn't work at all under my user account. Selection of non-horizontal lines works fine in either. Do you suggest I poke through the plist file for my account? It seems odd to think that the problem would manifest just for horizontal lines.

I haven't deleted preferences yet, but I did notice something: the length of the line is key. I can edit a .png, and add two lines, one short and one long. The short line will not be selectable, the long line will. Then I make the long line short and the short line long, and again, the (newly) short one cannot be selected and the (newly) long one can.