I am getting the following error trying to use boost::static_pointer_cast with shared_ptrs:

Error 19 error C2440: 'static_cast' : cannot convert from
'fusion::scene_graph::transform_graph::Light *const ' to
'fusion::scene_graph::transform_graph::Transform *'
c:\programming\lib\boost_1_34_0\boost\shared_ptr.hpp 199

The code that generates the error:

void Transform::DirtyTransformsVisitor::visitTransform(const TransformPtr &transform)
{
transform->dirtyTransform();
}

void Transform::DirtyTransformsVisitor::visitLight(const LightPtr &light)
{
visitTransform(boost::static_pointer_cast<Transform>(light));
}

The declarations:

class Transform; typedef boost::shared_ptr<Transform> TransformPtr;
class Drawable; typedef boost::shared_ptr<Drawable> DrawablePtr;
class Light; typedef boost::shared_ptr<Light> LightPtr;

class DirtyTransformsVisitor : public TransformVisitor
{
public:
void visitTransform(const TransformPtr &transform);
void visitLight(const LightPtr &light);
};

Has anyone got any idea why the pointer in my Light is const when the static_pointer_cast template is expanded?! I don't see why I should need to use a const_cast in this context, as non of the involved functions are const.
Thanks!