How to reproduce
1. Open the attached Project
2. Open the "Texture property Shader" Shadergraph
3. Change the default Texture of the "Texture to be updated" property to the "AnalyticsEventTracker icon"
4. Save the Shadergraph
5. Click on the "Texture property material" asset and observe the Inspector

Expected result: the default Texture is properly updated after saving the graph
Actual result: the default Texture stays the same

Reproduced in: 2018.2.0b6, 2018.2.0a4
Couldn't test with: 2018.2.0a3

Note: Tested on Shadergraph version 1.1.9