When making a property not exposed in Shader Graph, the default value is lost/reset

Repro steps:
* Download this project: [https://drive.google.com/file/d/1u2UPlJULOjRtKe-hwUOeKcOGXwvVUIu4/view?usp=sharing]
* Open the shader graph asset number 14
* Open the Sample Scene too - a sphere with the material using that shader graph shader should be loaded.

* select the color property and make it not exposed anymore

Expected result:
* the material in the scene should still have the blue outline, like the material preview in the shadergraph editor and like the previously set default value

Actual result:
* the material has no glow (as if the color property reverted to black instead)

Note: I tested this with 2023.2, 2023.1 and 2022.3. (all with their latest respective shadergraph packages) . This issues doesn't seem to be a regression.