SetRenderTexture called on property errors are thrown continuously on saving DefaultCompositionGraph after assigning Sample Virtual Texture node to Virtual Texture property.

Steps to repro:
1. Create a new HDRP template project
2. Windows > Render Pipeline > HD Render Pipeline Compositor.
3. Enable Compositor > Close the Compositor window.
4. Assets/Compositor/DefaultCompositionGraph > Open.
5. Blackboard > Add Virtual Texture > Drag it to Graph Editor.
6. Assign Sample Virtual Texture(VT) > Save the Graph.

Actual Result:
SetRenderTexture called on property errors in the console.

Expected Result:
No error in the console.

Reproducible in:
2020.2.0a18, 2020.1.0b16, 2020.1.0b13 with Package version 9.0.0 preview.33

Note: HDRP Compositor window introduced in 9.0.0 preview.33.

Environment:
Occurring only on Windows.

Stacktrace:
SetRenderTexture called on property 'Layer0' which is part of a stack. Stack values cannot be with render textures.
UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)