Are you referring to the cell borders, or to the shading on the first row and in the last cell? Cell B3 is also formatted with an 'inside' paragraph border.

You also have something strange going on with Styles in the document, which display as 預設段落字型1. You can clear that via Ctr-A, Ctrl-Spacebar, which returns everything to the Normal Style.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]