Forte 6U2 C++ compiler bug

Question

In the Forte 6U2 compiler, a function return can implicitly invoke a conversion constructor that is marked "explicit".
Consider:
class ABaseClass {};
template<class Type, class Uncert>
class Value
public:
     Value(Type const& t, Uncert const& u) : _t(t), _u(u) {}
protected:
     Type       _t;
     Uncert    _u;
class Foo : public Value<float, double>, public ABaseClass
public:
     explicit
     Foo(ABaseClass b=ABaseClass(), float val=-1, double tol=0)
         : ABaseClass(b), Value(val, tol)
         std::cerr << "Explicit constructed Foo\n";
class Bar : public Value<int, double>, public ABaseClass
public:
     explicit
     Bar(ABaseClass b=ABaseClass(), int val=-1, double tol=0)
         : ABaseClass(b), Value(val, tol)
         std::cerr << "Explicit constructed Bar\n";
class Context
public:
     Context() : _foo(ABaseClass(), 1.23, 0.45) {}
     Bar getFoo() const
         return _foo;
private:
     Foo _foo;
int main()
     Context c;
     c.getFoo();
}Note that Context::getFoo has a type mismatch between the declared return type and the return value. This is a bug that was not caught by the compiler. Intstead, Bar(static_cast<ABaseClass>(_foo)) is invoked and
returned. The output of this run is:
Explicit constructed Foo (Context constructor)
Explicit constructed Bar (Context::getFoo return)
This behavior is non-standards conforming.

Answer 1

-xO2 is enough to cause the failure.
Making the vulnerable pointer "static" fixes the problem, although this should make no difference.
My guess is over-eager register reuse, but I'm open to alternative theories.