Proposed resolution (approved by CWG 2025-11-07):

Change in 7.6.1.5 [expr.ref] bullet 8.6 as follows:

• Otherwise, if E2 designates a direct base class relationship (D, B) and D is either the cv-unqualified class type of E1 is cv T or a base class thereof, let cv be the cv-qualification of the type of E1. E1 is implicitly converted to the type "reference to cv D" (where the reference is an lvalue reference if E1 is an lvalue and an rvalue reference otherwise) and the expression designates the direct base class subobject of type B of the object designated by the converted E1. If E1 is an lvalue, then E1.E2 is an lvalue; otherwise, E1.E2 is an xvalue. The type of E1.E2 is “cv B” cv B. [Note 6: This can only occur in an expression of the form e1.[:e2:]. —end note]

Subclause 7.6.1.5 [expr.ref] bullet 8.6 does not specify what happens if the direct base class relationship originates from an unambiguous base class of E1.