Clone-by-dragging doesn't snap to source shape, but snaps to others.

When cloning shapes using Alt+drag, the cloned shape does not snap to the shape that spawned it, though it *does* snap to other shapes in the mockup.

For example, start a new mockup and create a checkbox button. Then Alt+drag that checkbox button and notice that no snapping occurs. Release the mouse button to create the copy. Now Alt+drag to produce a third copy and notice which of the two existing buttons it snaps to.