If the entire view is displayed with a header in the embedded view, it can be re-sorted by another column that has it set. However, if show single category is set, the triangle for sorting will disappear. This is because it would turn off the categorization that determines the selection of displayed documents.
But users need this sorting. Embedded views typically display only small numbers of documents, so this feature could run on the Notes client.
The same would be useful in a view in a PickListCollection with a Singlecategory parameter.