Dithering controls don't get applied automatically on startup with 340.32

After an update to 340.32, I’m getting ugly gradients (they look like 16bit colour) on my laptop’s internal display. When connecting an external display on the VGA port and moving a window from one window to the other, the gradients are fine. I did some digging and found this:
I don’t know how relevant to my problem this is, but after reading about dithering to 8bpc or 6bpc, I went into nvidia-settings -> DFP-1 -> Controls -> Dithering Controls and changed depth to 6bpc from Auto. This instantly corrected the issue. However, on reboot gradients are still looking bad and after I login, I have to run nvidia-settings and the problem disappears before the GUI window is even rendered, but if I don’t run it at all, the problem doesn’t disappear. I tried running nvidia-persistenced on startup from a shell script, but even though that ran, the problem didn’t go away.
Is this a bug, a product of some kind of a limitation or expected and how can I fix this issue?


See Option “FlatPanelProperties” “string” in ftp://download.nvidia.com/XFree86/Linux-x86_64/340.32/README/xconfigoptions.html

I looked at the docs, but I see no way to control the Dithering Depth (8bpc, 6bpc or auto).
I tried adding a 10-nvidia.conf to /etc/X11/xorg.conf.d with the following contents:

Section "Device"
    Identifier  "NVIDIA GT 755M"
    Driver      "nvidia"
    BusID       "PCI:1:0:0"
    Option      "FlatPanelProperties" "DitheringDepth=6bpc"

but that didn’t work (I expected, as that property is not listed in the readme.

Apologies if I’m missing something obvious here.