In the color scheme editor:
Choose "Black on Random Light" and click on Edit, disable "Randomly adjust colors for each session", and click OK.
It's saved correctly now, previously it stayed on.
Alternatively, select some other color scheme, enable the option and click OK. Then try to disable it again. This works now, previously it also stayed on.
Select an existing colorscheme and click on New, the new color scheme still properly inherits the "Randomly adjust colors for each session" setting. (this actually worked before, which I find slightly surprising... ;-) )