Unlike regular colors added in the document or app palette, gradient color swatch assignments made e.g. for object fill, are not reflected in the palette anyway (the swatch is not highlighted, though the gradient is collrectly applied for the selected object). For regular colors (both local and global swatches) you can see the color assignment when selecting objects that have color attributes given by using swatches. Also, it does not seem that it is possible to edit a gradient swatch so probably this is just a feature that has not been developed to the full, rather than a bug.