If you drag a block drawing to the quilt, and it seems to disappear, do this:
Explanation: “Outline Patches” and “Outline Blocks” are checked by default. But you can uncheck them. When “Outline Patches” and “Outline Blocks” are unchecked, you cannot see patch lines or block outlines. A block drawing is only lines. So setting a line drawing is invisible until you choose to show the lines on the quilt.