When shaders are switched for materials, their custom Render Queue is reset to default shader value.

Steps to reproduce:
1) Open the attached project.
2) In the Assets folder, select 'Mat' material.
- In the Inspector, notice that the shader for this material is set to 'Mobile/Bumped Diffuse'.
- The custom Render Queue is set to 'Custom: 2050'.
3) Select any shader for the material, via the 'Shader' dropdown in the Inspector.

Selecting any shader, even the same shader that is already selected resets the custom Render Queue to 2000 (From Shader).

Expected result: custom Render Queue remains unchanged when switching shaders.
Actual result: custom Render Queue gets reset when switching shaders.

Reproduced on:
2017.1.0b3, 5.5.3p2, 5.5.0f3