Word heading number blacked out

When opening the document I am working on in Word 2010 this morning, the number in heading level 1 is a black rectangle:

however, it still look ok in the bookmark pane:

Weird, ey?

1. Place the cursor just to the right of the black box in any example of the affected heading.
2. Hit ← (left arrow) and the black box should turn gray.
3. Type Ctrl+Shift+S to bring up a style popup.
4. Click Reapply.

This has worked every time I've had this problem.

I solved this after all, I also noticed that someone else was unable to resolve this on a Microsoft forum, so if you read this, here is my solution:

1. Press properties for Heading 1
2. Press format, numbering
3. Chose No numbering. Exit the properties. All numbering will now disappear.
4. From the "start" pane, press multi-level-list, and then the format that looks like:

1. Heading 1

1.1. Heading 2

1.1.1. Heading 3