I edit the model brightness to be "-50"... and the slider is moved to the 1/4 point on the slider scale (OK), and the spinner is set to -50 (OK).
I save the settings with the [OK] button.
I go back into the edit screen for the model, and find that the slider is still positioned to the 1/4 point on the scale (OK), but the value in the spinner box is set to 0 (WRONG).
So, I think the value is being set and preserved, otherwise the slider would be positioned back to the center. I think the spinner control is not being set to -50.
Pictures below...
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