It sounds like the underlying style is set to automatically update. The
method for turning this off varies depending on which version of Word you're
using. In Word 2003, choose Format - Styles and Formatting. Click in the
table in a cell/row that exhibits the problem so that the corresponding
style shows up in the Style dropdown. In the Styles & Formatting task pane,
right-click on the style, and choose Modify. In the Modify Style dialog box,
remove the check next to Automatically Update.