GetRenderTargetData problems with multiple render targets

// "finalTex" is the texture to which the other surface is attached
D3DDev->CreateTexture( width, height, 1, D3DUSAGE_RENDERTARGET,
	D3DFMT_A8R8G8B8, D3DPOOL_DEFAULT, &finalTex, 0 );

// "lockTex" is the texture to which the lockable surface is attached
D3DDev->CreateTexture( width, height, 1, 0,
	D3DFMT_A8R8G8B8, D3DPOOL_SYSTEMMEM, &lockTex, 0 );
	
/* ...rendering stuff... */

// Setting up the targets for the final render pass
D3DDev->SetRenderTarget(0, D3DBackBuffer);

finalTex->GetSurfaceLevel(0, &finalSurf);
D3DDev->SetRenderTarget(1, finalSurf);

/* ...final render pass... */

// Put render data in the lockable surface
lockTex->GetSurfaceLevel(0, &lockSurf);

finalTex->GetSurfaceLevel(0, &finalSurf);	// using this render target creates the problem

D3DDev->GetRenderTargetData(finalSurf, lockSurf);

// Save the surfaces to a file for proof
D3DXSaveSurfaceToFile(L"outFinalSurf.jpg", D3DXIFF_JPG, finalSurf, NULL, NULL);
D3DXSaveSurfaceToFile(L"outLockSurf.jpg", D3DXIFF_JPG, lockSurf, NULL, NULL);

D3DDev->GetBackBuffer(0, 0, D3DBACKBUFFER_TYPE_MONO, &finalSurf);