If you have bought OpenSprinkler 2.3 recently, those LCD settings are irrelevant now, because the recent batches of OpenSprinkler 2.3 use I2C LCD, where the contrast and backlight cannot be changed in software (except that the backlight can be turned off in software). We should probably change the UI to hide these settings if such LCDs are detected.
That would explain things. I purchased a new OpenSprinkler late last year after my original one got fried in a storm and wanted to have the backlight on permanently like I previously did as it lives in a dark garage. Personally I would like to see a return of this functionality.