System Parameters default theme possible bug

[daveparrish]

Same thing here I have two installs one production and one lab both versions are 4.12.3 the lab version dose not have the option in System settings for Default Theme and has no problem when saving the system settings not sure where to make this available any help would be appreciated.
The production server has the Default Theme option and without changing any settings and click the save I get the same issue where it writes to the configuration file just as Archer62 is showing in his configuration file.