How do I stop OpenOffice.org from generating a black line from hash characters?

A series of '#' characters on a line by themselves has generated a bold black double line. How can I remove this line?

A series of # symbols (hash characters) is a keyboard shortcut to creating a solid line below a paragraph in a text document. To remove this line, click anywhere in the paragraph just above the thick line and choose Format > Paragraph. The line set will appear on the Borders tab. To remove the line, keep the cursor in the paragraph above the line and choose Format > Default.