This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 112c. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
According to 11.8.5 [class.protected] paragraph 1, except when forming a pointer to member,
All other accesses involve a (possibly implicit) object expression (220.127.116.11 [expr.ref]).
It is not clear that this is strictly true for the invocation of a base class constructor from a mem-initializer. A wording tweak may be advisable.