This is actually a bug in firmware 2.1.6, and I apologize for it. Basically since a little while back we’ve switched to use I2C LCD, and these types of LCDs don’t allow changing contrast or brightness (but it does allow turning backlight on/off). The ‘dimming’ parameter supposedly can be used to keep the backlight on (if the dimming value is more than 0, it keeps the backlight on). But due to a bug in firmware 2.1.6, it ignores the dimming value for I2C LCD. We have started working on firmware 2.1.7 and it has been addressed there.
If you need this to be fixed right now, we can send you a custom firmware with this issue fixed. Otherwise, if this is not urgent, please wait for firmware 2.1.7. Thanks.