Brightness fn keys only work to lower brightness

[Gordon Ball]

Ubuntu GNOME 14.04, with ppa:gnome3-team/gnome3
gnome-shell 3.10.4-0ubuntu5
Graphics: i915
lspci: 00:02.0 VGA compatible controller: Intel Corporation Haswell-ULT Integrated Graphics Controller (rev 09)

Screen brightness can be adjusted successfully using the Control Panel > Brightness and Lock slider.

/sys/class/backlight/acpi_video0/max_brightness -> 100

When using the FN keys (keycodes 224, 225 for down, up respectively), the brightness OSD is shown in both cases, but only trying to reduce the brightness actually results in a change of brightness - attempting to increase it causes the screen to flicker once but does not increase the brightness.

Pressing reduce brightness once gives:

/sys/class/backlight/acpi_video0/brightness -> 85
/sys/class/backlight/acpi_video0/actual_brightness -> 80

And continues in steps of (brightness, actual_brightness) of (65, 60), (45, 40), (25, 20), (5, 0) and finally (0, 0). From (0, 0) the increase brightness button works to increase the brightness to (5, 0), but no further. Some edge case related to the difference in brightness and actual_brightness?

Conceivably related to GNOME bug #710380?