Word 2000 Formatting

Using Word 2000, we have found that highlighting a specific word, phrase, sentence, or paragraph, and changing the formatting for that selection will cause the formatting of the entire document to change. For example, if I want to bold only a phrase in a document, highlight that phrase and click the Bold button, the entire document becomes bold. By clicking the Undo button, everything except the highlighted section reverts to it prior formatting.

The only thing I can find from MS’s KB’s isto select all but the LAST character to be changed, make the changes, then select the last character and make those changes.

Does anyone have any suggestions to ‘fix’ this or have you encountered this? If so, what are you doing to fix it?