scene became a mess when I drew mirror reflection(dx9) - directx

Question

In my project, I draw a house, which consists of wall, floor, mirror, a switch to turn on or turn off the fire system. Everything is going on well by here.
At last, I want to draw a person's reflection on the mirror, but after I add the drawReflection function, things go wrong, scene became a mess. Why? I write the function according to the book.
void House::draw(float timeDelta)
{
_device->SetFVF(d3d::Vertex::FVF);
_device->SetStreamSource(0, _vb, 0, sizeof(d3d::Vertex));
// draw wall
_device->SetMaterial(&d3d::WHITE_MTRL);
_device->SetTexture(0, _wall);
_device->DrawPrimitive(D3DPT_TRIANGLELIST, 0, 10);
// draw floor
_device->SetMaterial(&d3d::WHITE_MTRL);
_device->SetTexture(0, _floor);
_device->DrawPrimitive(D3DPT_TRIANGLELIST, 30, 2);
// draw mirror
_device->Clear(0, NULL, D3DCLEAR_ZBUFFER, 0, 1.0f, 0);
_device->SetRenderState(D3DRS_ALPHABLENDENABLE, true);
_device->SetRenderState(D3DRS_SRCBLEND, D3DBLEND_ONE);
_device->SetRenderState(D3DRS_DESTBLEND, D3DBLEND_ZERO);
_device->SetMaterial(&d3d::WHITE_MTRL);
_device->SetTexture(0, _mirror);
_device->DrawPrimitive(D3DPT_TRIANGLELIST, 36, 2);
_device->SetRenderState(D3DRS_ALPHABLENDENABLE, false);
// draw switch button
D3DXMATRIX T, Ry, P;
D3DXMatrixTranslation(&T, -4.95f, 2.0f, 3.0f);
D3DXMatrixRotationY(&Ry, D3DX_PI * 1.5f);
P = Ry * T;
_device->SetTransform(D3DTS_WORLD, &P);
_device->SetMaterial(&d3d::BLUE_MTRL);
_device->SetTexture(0, NULL);
_switch->DrawSubset(0);
// draw fire system
D3DXMATRIX I;
D3DXMatrixIdentity(&I);
_device->SetTransform(D3DTS_WORLD, &I);
if(_fSwitchOn)
{
if(_fs->isDead())
_fs->reset();
_fs->update(timeDelta);
_fs->render();
}
// draw reflection of person
//drawReflection();
}
But after I add drawReflection() function to it, it became a mess. Why?
drawReflection() function is below:
void House::drawReflection()
{
// enable stencil
_device->SetRenderState(D3DRS_STENCILENABLE, true);
_device->SetRenderState(D3DRS_STENCILFUNC, D3DCMP_ALWAYS);
_device->SetRenderState(D3DRS_STENCILREF, 0x1);
_device->SetRenderState(D3DRS_STENCILMASK, 0xffffffff);
_device->SetRenderState(D3DRS_STENCILWRITEMASK, 0xffffffff);
_device->SetRenderState(D3DRS_STENCILZFAIL, D3DSTENCILOP_KEEP);
_device->SetRenderState(D3DRS_STENCILFAIL, D3DSTENCILOP_KEEP);
_device->SetRenderState(D3DRS_STENCILPASS,
D3DSTENCILOP_REPLACE);
// stop write to target buffer and depth buffer
_device->SetRenderState(D3DRS_ALPHABLENDENABLE, true);
_device->SetRenderState(D3DRS_SRCBLEND, D3DBLEND_ZERO);
_device->SetRenderState(D3DRS_DESTBLEND, D3DBLEND_ONE);
_device->SetRenderState(D3DRS_ZWRITEENABLE, false);
// draw the mirror to stencil buffer
_device->SetFVF(d3d::Vertex::FVF);
_device->SetStreamSource(0, _vb, 0, sizeof(d3d::Vertex));
_device->SetMaterial(&d3d::WHITE_MTRL);
_device->SetTexture(0, _mirror);
D3DXMATRIX I;
D3DXMatrixIdentity(&I);
_device->SetTransform(D3DTS_WORLD, &I);
_device->DrawPrimitive(D3DPT_TRIANGLELIST, 36, 2);
_device->SetRenderState(D3DRS_ZWRITEENABLE, true);
// transform the mesh
_device->SetRenderState(D3DRS_STENCILFUNC, D3DCMP_EQUAL);
_device->SetRenderState(D3DRS_STENCILPASS, D3DSTENCILOP_KEEP);
D3DXMATRIX Reflect, S, T, P;
D3DXPLANE plane(0.0f, 0.0f, 1.0f, -5.0f);
D3DXMatrixReflect(&Reflect, &plane);
// D3DXMatrixScaling(&S, 0.2f, 0.2f, 0.2f);
D3DXVECTOR3 pos;
_person->getPosition(&pos);
D3DXMatrixTranslation(&T, pos.x, pos.y, pos.z);
P = T * Reflect;
_device->Clear(0, NULL, D3DCLEAR_ZBUFFER, 0xffffffff, 1.0f, 0);
_device->SetRenderState(D3DRS_SRCBLEND, D3DBLEND_DESTCOLOR);
_device->SetRenderState(D3DRS_DESTBLEND, D3DBLEND_ZERO);
_device->SetRenderState(D3DRS_CULLMODE, D3DCULL_CW);
_device->SetTransform(D3DTS_WORLD, &P);
_person->draw();
_device->SetRenderState(D3DRS_CULLMODE, D3DCULL_CCW);
_device->SetRenderState(D3DRS_STENCILENABLE, false);
_device->SetRenderState(D3DRS_ALPHABLENDENABLE, false);
}