[Moved to DR at the February, 2014 meeting.]

Proposed resolution (September, 2013):

Change 6.5.4 [basic.lookup.argdep] paragraph 2 as follows:

...The sets of namespaces and classes are determined in the following way:

• ...

• If T is a class type (including unions), its associated classes are: the class itself; the class of which it is a member, if any; and its direct and indirect base classes. Its associated namespaces are the innermost enclosing namespaces of which its associated classes are members. Furthermore..

• If T is an enumeration type, its associated namespace is the innermost enclosing namespace in which it is defined of its declaration. If it is a class member, its associated class is the member's class; else it has no associated class.

• ...

This resolution also resolves issues 1690 and 1692.

According to 6.5.4 [basic.lookup.argdep] paragraph 2,

If T is an enumeration type, its associated namespace is the namespace in which it is defined. If it is class member, its associated class is the member's class; else it has no associated class.

This does not take into account opaque enumerations, which can be defined in an enclosing namespace of the one of which is a member.