For Word 2003 & earlier, with the Drawing toolbar visible, click on the Select Objects tool. This is normally the second tool from the left and looks like a large mouse pointer. If you then click over the shape that has the 'behind text' format, it will be selected.

For Word 2007 & later you'll find an 'Editing' panel at the right-hand end of the Ribbon's Home tab. In that is a 'Select' dropdown. From that, choose 'Select Objects'. If you then click over the shape that has the 'behind text' format, it will be selected.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]