Removing Favorite Shape Styles from OmniGraffle Inspector

I was testing custom shapes by creating them and adding them via “Add to Favorite Shape Styles” from the shape’s right-click popup menu. Then, in the Shape section of the Object inspector, they appear in the popup. However, now I can’t remove them.

According to the documentation here, they can be removed from the style well, but they remain in the shape popover. I didn’t see any relevant information in the shape inspector section.