UMLR — Description of Generalization of Enumerations is contradictory

The specification says:

An instance of a Classifier is also an (indirect) instance of each of its generalizations.

This means that the run-time extension of a general Classifier includes the extension of the specific Classifier: All instances of Rectangle are also instances of Polygon.
Now it says about Enumeration:

An EnumerationLiteral defines an element of the run-time extension of an Enumeration.

Taken together this means that all EnumerationLiterals of a specific Enumeration (its run-time extension) must also be contained in the set of Literals of the general Enumeration.
Finally it says about Enumeration specialization:

An Enumeration that specializes another may define new EnumerationLiterals that are not defined in the generalizing Enumeration.

This is a contradiction. The extension of a specific Classifier must always be smaller than that of the general Classifier.
I agree that this makes the specialization of Enumerations unusable for a lot of purposes. However I don't see how this could get changed.