Word Duplicate-Paragraph Bug

Occasionally I encounter a strange bug in Microsoft Word 2010. Consider the following document part:

This box contains six paragraphs:

1. Header "Lemma"
2. Line with word "Let"
3. Equation
4. Line with text "be the gravitational field. Then"
5. Equation
6. Line with text "for any closed surface S enclosing the origin."

However, for some reason, the fourth line is rendered twice. If I edit the fourth line, the 'ghost line' is updated simultaneously. And, as you can see, if I select a part of the fourth line, the selection is also drawn on the 'ghost line'.

Is there any way of removing the ghost line?

I fixed this by deleting the endline before the first instance. This caused my the previous line and the first instance to append, and the second instance to disappear completely.

The issue is resoved (in my case) by removing the 'Keep lines together' option in the paragraph settings.

But, clearly, this is a bug (one of many in Word 2007 and 2010...). Now, it isn't terribly important for me to have this paragraph setting on in this style, so I can live without it in this case.

If you want to experiment yourself with this issue, have a look at

• http://privat.rejbrand.se/WordGhostLine.docx

The following additional details seem to work for Word 2007.

The 'Keep lines together' option must be unchecked for all lines containing equations. Other lines with text may have the 'Keep lines together' option checked without causing paragraph duplication.

Another indicator of the problem is misplaced equation highlighting as the mouse is moved around and near the lines containing equations.