Steps to reproduce:

• Create a 3D project
• Create a new default material
• Create a new state "State1" and select it
• Select first default material and change it's diffuse color
• Copy all material properties of first default material
• Paste material properties to second default material
• Select Base State
• -> both preview images in Material Browser are not updated to show the preview for the current selected state, only the preview for the selected material. Would expect all material preview to update when switching between states. 
• See attached recording