I think this is a Zend incompatibility.

interface MyReflectionInterface
{
    public function toString();
}

class MyReflectionMethod extends ReflectionMethod implements ReflectionInterface
{
    public function toString()
    {
        return parent::__toString();
    }
}

I get:

Fatal error: Cannot override final method ReflectionMethod::toString()

If I remove the toString() implementation, then both Zend PHP and HHVM fail:

• HHVM: "Fatal error: Access level to MyMethodReflection::toString() must be public"
• PHP: "Fatal error: Class Zend\Code\Reflection\MethodReflection contains 1 abstract method and must therefore be declared abstract or implement the remaining methods (Zend\Code\Reflection\ReflectionInterface::toString)"

This is an issue in Zend Framework 2: zendframework/zendframework#6418