This feature of Word causes changes to a style definition when someone applies an explicit formatting change to something in the document. First of all, you need to check to make sure that all users have dynamic style updating turned off.
There are a couple of things to check when this happens.
If Don saves a file with certain styles in place and someone else with access to the server opens and saves the same file, then when Don subsequently opens the file, invariably the style definitions have changed. It seems that when there are multiple authors using a single document, the styles sometimes change unexpectedly. Don has run into a problem in his office regarding styles.
