I recently saw a question regarding line breaks in the table of contents – OpenOffice does not allow you to edit a table of contents except through styles. Sometimes the way that long headings are formatted might not be what you desire.
One thing to note about the TOC is that the line breaks that you insert in the heading itself will be reflected in the TOC.
Putting in a manual line break (Shift + Enter) in this heading:
will result in a line break appearing in the Table of Contents: