Explicit specialization of member class template

The following code compiles with VC8
but fails to compiles with Comeau online,

[Error
"ComeauTest.c", line 7: error: explicit specialization is not allowed in the
           current scope
    template <>
    ^

"ComeauTest.c", line 10: error: explicit specialization is not allowed
in the
           current scope
    template <>
    ^
End-Error]

I locate the standard here:

[STD
14.7.3 Explicit specialization [temp.expl.spec]
An explicit specialization of any of the following:
?? function template
?? class template
?? member function of a class template
?? static data member of a class template
?? member class of a class template
?? member class template of a class template
?? member function template of a class template
can be declared by a declaration introduced by template<>

End-STD]

if I didn't get it wrong, we can have member class template explicit
specialization if the outter class is not templated. Right?

///////////////////////////////////////////

struct A
{
private:
     template <class T>
     struct HasConvertionTo;

     template <>
     struct HasConvertionTo<long> {};

     template <>
     struct HasConvertionTo<bool> {};

public:
template <class T>
     operator T () const
     {
         return Convert(HasConvertionTo<T>()); // CT error trigger
     }

private:
     template <class T>
     T Convert(HasConvertionTo<T>) const // dispatcher
     {
         return Convert(T());
     }

     long Convert(long) const
     {
         return 10;
     }

     bool Convert(bool) const
     {
         return true;
     }
};

int main()
{
     A a;

     long l = a;

     if (a) {
     }
}
--
Thanks
Barry