Without actually seeing the problem document, it can be difficult for anyone to diagnose the issue. The most likely explanation is that the headings have different tab-stops. If that's not the cause, can you attach a document to a post with some representative data (delete anything sensitive)? You do this via the paperclip symbol on the 'Go Advanced' tab at the bottom of this screen.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]

Thanks for your reply. I have checked under Modify Style and then under Tabs, but the tab stops for all my headers are empty and clear (Alignment Left & Leader None). Is there anywhere else I can check for this to see if this is the cause?