Problem MCVE for Urho3D instancing issue

ProblemMCVE.cpp

// Enable this to work around the problem.
//#define COMPILE_WORKAROUND

#ifdef _MSC_VER
#pragma warning( disable : 4005 ) // macro redefinition for URHO3D_STATIC_DEFINE and URHO3D_SSE in <Urho3D/Urho3D.h>
#endif
#include <Urho3D/Urho3D.h>
#include <Urho3D/Core/CoreEvents.h>
#include <Urho3D/Engine/Application.h>
#include <Urho3D/Input/Input.h>
#include <Urho3D/Resource/ResourceCache.h>
#include <Urho3D/Scene/Scene.h>
#include <Urho3D/Graphics/Camera.h>
#include <Urho3D/Graphics/Renderer.h>
#include <Urho3D/Graphics/DebugRenderer.h>
#include <Urho3D/Graphics/Octree.h>
#include <Urho3D/Graphics/Model.h>
#include <Urho3D/Graphics/StaticModel.h>
#include <Urho3D/Graphics/Material.h>
#include <Urho3D/Graphics/Zone.h>
#ifdef _MSC_VER
#pragma warning( default : 4005 )
#endif

using namespace Urho3D;

class ProblemMCVE : public Application
{
public:
	SharedPtr<Scene> scene_;
	Node* cameraNode_;
	Urho3D::Camera* camera_;

	/*
		Any pair of objects with same model *and* material will be disappearing and reappearing as the camera is moved.
		Workaround: ->Clone() the material.
	*/
	SharedPtr<Node> node_a; // okay (Sphere+Stone)
	SharedPtr<Node> node_b; // okay (Sphere+default)
	SharedPtr<Node> node_c; // disappearing (Sphere+Mushroom)
	SharedPtr<Node> node_d; // disappearing (Sphere+Mushroom)
	// ... if the model of (say) d is changed, then c&d work, even with the same (non-cloned) material!

	ProblemMCVE(Context* context) : Application(context) { }

	virtual void Setup()
	{
		engineParameters_["FullScreen"] = false;
		engineParameters_["WindowWidth"] = 1280;
		engineParameters_["WindowHeight"] = 720;
		engineParameters_["WindowResizable"] = true;
	}

	virtual void Start()
	{
		ResourceCache* cache=GetSubsystem<ResourceCache>();

		scene_=new Scene(context_);
		scene_->CreateComponent<Octree>();
		//scene_->CreateComponent<DebugRenderer>();

		cameraNode_=scene_->CreateChild("Camera");
		camera_=cameraNode_->CreateComponent<Camera>();

		Renderer* renderer=GetSubsystem<Renderer>();
		SharedPtr<Viewport> viewport(new Viewport(context_,scene_,cameraNode_->GetComponent<Camera>()));
		renderer->SetViewport(0,viewport);

		// Note: Problem remains even without the zone, but I've kept it because otherwise, things are hard to see.
		Node* zoneNode=scene_->CreateChild("Zone");
		Zone* zone=zoneNode->CreateComponent<Zone>();
		zone->SetBoundingBox(BoundingBox(-50000.0f, 50000.0f));
		zone->SetFogStart(500.0f);
		zone->SetFogEnd(600.0f);
		zone->SetFogColor(Color(0.0f, 0.0f, 0.0f));
		zone->SetAmbientColor(Color(1.0f, 1.0f, 1.0f));

		SubscribeToEvent(E_KEYDOWN, URHO3D_HANDLER(ProblemMCVE, HandleKeyDown));
		SubscribeToEvent(E_UPDATE, URHO3D_HANDLER(ProblemMCVE, HandleUpdate));

		cameraNode_->SetPosition(Vector3(0.0f, 0.0f, 0.0f));
		cameraNode_->SetDirection(Vector3::FORWARD);

		{
			node_a = scene_->CreateChild();
			node_a->SetPosition(Vector3(0.0f, 1.6f, 6.0f));
			StaticModel* boxObject = node_a->CreateComponent<StaticModel>();
			boxObject->SetModel(cache->GetResource<Model>("Models/Sphere.mdl"));
			boxObject->SetMaterial(cache->GetResource<Material>("Materials/Stone.xml"));
		}
		{
			node_b = scene_->CreateChild();
			node_b->SetPosition(Vector3(0.0f, 10.0f, 6.0f));
			StaticModel* boxObject = node_b->CreateComponent<StaticModel>();
			boxObject->SetModel(cache->GetResource<Model>("Models/Sphere.mdl"));
		}
#ifdef COMPILE_WORKAROUND
		Material* mtlC;
#endif
		// disappearing without workaround
		{
			node_c = scene_->CreateChild();
			node_c->SetPosition(Vector3(0.0f, 6.0f, 6.0f));
			StaticModel* boxObject = node_c->CreateComponent<StaticModel>();
			boxObject->SetModel(cache->GetResource<Model>("Models/Sphere.mdl"));
#ifdef COMPILE_WORKAROUND
			mtlC = cache->GetResource<Material>("Materials/Mushroom.xml");
			boxObject->SetMaterial(mtlC);
#else
			boxObject->SetMaterial(cache->GetResource<Material>("Materials/Mushroom.xml"));
#endif
		}
		// disappearing without workaround
		{
			node_d =scene_->CreateChild("Planet");
			node_d->SetPosition(Vector3(-4.0f, 1.6f, 6.0f));
			node_d->SetScale(2);
			StaticModel* boxObject = node_d->CreateComponent<StaticModel>();
			boxObject->SetModel(cache->GetResource<Model>("Models/Sphere.mdl"));
#ifdef COMPILE_WORKAROUND
			boxObject->SetMaterial(mtlC->Clone());
#else
			boxObject->SetMaterial(cache->GetResource<Material>("Materials/Mushroom.xml"));
#endif
		}
	}

	virtual void Stop()
	{
	}

	void HandleUpdate(StringHash eventType,VariantMap& eventData)
	{
		float timeStep=eventData[Update::P_TIMESTEP].GetFloat();

		// Movement speed as world units per second
		float MOVE_SPEED=10.0f;
		// Mouse sensitivity as degrees per pixel
		const float MOUSE_SENSITIVITY=0.1f;

		// camera movement
		Input* input=GetSubsystem<Input>();
		if(input->GetQualifierDown(1))  // 1 is shift, 2 is ctrl, 4 is alt
			MOVE_SPEED*=10;
		if(input->GetKeyDown('W'))
			cameraNode_->Translate(Vector3(0,0, 1)*MOVE_SPEED*timeStep);
		if(input->GetKeyDown('S'))
			cameraNode_->Translate(Vector3(0,0,-1)*MOVE_SPEED*timeStep);
		if(input->GetKeyDown('A'))
			cameraNode_->Translate(Vector3(-1,0,0)*MOVE_SPEED*timeStep);
		if(input->GetKeyDown('D'))
			cameraNode_->Translate(Vector3( 1,0,0)*MOVE_SPEED*timeStep);

		if(!GetSubsystem<Input>()->IsMouseVisible())
		{
			IntVector2 mouseMove=input->GetMouseMove();
			if(mouseMove.x_>-2000000000&&mouseMove.y_>-2000000000)
			{
				static float yaw_=0;
				static float pitch_=0;
				yaw_+=MOUSE_SENSITIVITY*mouseMove.x_;
				pitch_+=MOUSE_SENSITIVITY*mouseMove.y_;
				pitch_=Clamp(pitch_,-90.0f,90.0f);
				// Reset rotation and set yaw and pitch again
				cameraNode_->SetDirection(Vector3::FORWARD);
				cameraNode_->Yaw(yaw_);
				cameraNode_->Pitch(pitch_);
			}
		}
	}

	void HandleKeyDown(StringHash eventType,VariantMap& eventData)
	{
		using namespace KeyDown;
		int key=eventData[P_KEY].GetInt();

		if(key==KEY_TAB)
		{
			GetSubsystem<Input>()->SetMouseVisible(!GetSubsystem<Input>()->IsMouseVisible());
			GetSubsystem<Input>()->SetMouseGrabbed(!GetSubsystem<Input>()->IsMouseGrabbed());
		}
		else if(key==KEY_ESCAPE)
			engine_->Exit();
		else if(key==KEY_T)
			camera_->SetFillMode(camera_->GetFillMode()==FILL_WIREFRAME?FILL_SOLID:FILL_WIREFRAME);
	}
};

URHO3D_DEFINE_APPLICATION_MAIN(ProblemMCVE)