gsd-power: nvidia: Screen dims after 15 seconds even when dimming disabled

[Matthew D. Mower]

Ubuntu GNOME 17.04 64bit
Lenovo Thinkpad Yoga 14
- Intel i5-6200U (HD Graphics 520) with nVidia GeForce 940M (GM108M)

When using the nvidia binary driver (have tested nvidia-367, nvidia-376, nvidia-384), my screen dims after 15 seconds regardless of the setting:

Settings > Power: Dim screen when inactive = OFF

This dimming only occurs when I'm running from battery; it does not occur on AC. I've verified that the settings dialog does correctly update /org/gnome/settings-daemon/plugins/power/idle-dim to false, but it doesn't seem to be respected.

As a workaround, I change /org/gnome/settings-daemon/plugins/power/idle-brightness to 100 and the dimming no longer occurs. Setting values lower than 100 causes dimming to occur (and 30 is less bright than 60, for example). Using this workaround, in /var/log/syslog I see: "gsd-power[1883]: gsd_power_backlight_percentage_to_abs: assertion 'value <= 100' failed".