Steps to reproduce:
1. Open attached “Materials.zip” Unity project
2. Open “Main” scene
3. Change object order in Scene (or make any other change to enable scene saving)
4. Save Scene

Expected results:
Nothing unusual happens and Render Texture in scene continues being rendered
Actual results:
Render Texture is no longer rendered and material properties cannot be accessed

Reproduced in 2018.1.0b1, 2017.3.0f3, 2017.2.1p1, 2017.1.2p4, 5.6.5f1, 5.6.0f1

Note: Reopening scene will make Material properties accessible again
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By design:
Property needs to be declared as a serialized type