Steps To Reproduce:
1. Create a Project with LWRP/HDRP template.
2. Project > Shaders > PBR Graph
3. Click on the + icon on blackboard and create a property(Vector 3 for ex).
4. Drag and drop the property in the shader graph window.
5. Duplicate the property 4-5 times
6. Hit ctrl+z continuously for 4-5 times

Expected Result
The duplicated properties should be removed.

Observed Result:
Errors are thrown in the console

Note: The properties can't be deleted once the bug occurs.

Stack Trace:
Exception: Trying to retrieve a node that was removed from the graph.
UnityEditor.ShaderGraph.AbstractMaterialGraph.GetNodeFromTempId (UnityEditor.ShaderGraph.Identifier tempId) (at Library/PackageCache/com.unity.shadergraph@5.2.3/Editor/Data/Graphs/AbstractMaterialGraph.cs:495)
UnityEditor.ShaderGraph.Drawing.PreviewManager.PropagateNodeSet (UnityEditor.ShaderGraph.Drawing.IndexSet nodeSet, System.Boolean forward, System.Collections.Generic.IEnumerable`1[T] initialWavefront) (at Library/PackageCache/com.unity.shadergraph@5.2.3/Editor/Drawing/PreviewManager.cs:136)
UnityEditor.ShaderGraph.Drawing.PreviewManager.RenderPreviews () (at Library/PackageCache/com.unity.shadergraph@5.2.3/Editor/Drawing/PreviewManager.cs:216)
UnityEditor.ShaderGraph.Drawing.GraphEditorView.HandleGraphChanges () (at Library/PackageCache/com.unity.shadergraph@5.2.3/Editor/Drawing/Views/GraphEditorView.cs:382)
UnityEditor.ShaderGraph.Drawing.MaterialGraphEditWindow.Update () (at Library/PackageCache/com.unity.shadergraph@5.2.3/Editor/Drawing/MaterialGraphEditWindow.cs:147)
UnityEditor.EditorApplication:Internal_CallUpdateFunctions()

Reproducible On: 5.2.3, 2.0.1 (Shader graph packages before 2.0.1 were broken)

Checked on unity version: 2019.1.0b3

Environment:
Occurs only on mac.