Proposed resolution (September, 2015):

Change 9.9.2 [namespace.def] paragraph 3 as follows:

In a named-namespace-definition, the identifier is the name of the namespace. If the identifier, when looked up (6.5.3 [basic.lookup.unqual]), refers to a namespace-name (but not a namespace-alias) that was introduced in the declarative region namespace in which the named-namespace-definition appears or that was introduced in a member of the inline namespace set of that namespace, the namespace-definition extends the previously-declared namespace. Otherwise, the identifier is introduced as a namespace-name into the declarative region in which the named-namespace-definition appears.