LibreWriter borders change size

I put LibreOffice 4.1.5 Stable on my mother’s new Win7 computer replacing her old XP Word 2000. Within 1 day she seems to have found a bug that I haven’t found mentioned here. She discovered the feature where a repeated string of asterisks gets changed to a line stretching across the page. The problem is that after that document was saved (doc format) and then reopened, that thin line changed to a 9pt line that printed about 3/8" wide. I tried installing LibreOffice on my Win7 laptop and experienced the same behavior. First, is there a way to prevent the automatic line, and is there a way to prevent it from changing size?