Sorry I think you are missing the point of what I said...
If you set the BG colour to 64 via the pop-up colour selection, that will be wrong.
But it looks like that is not your issue, as it seems you have set the BG colour to 16 via the pop-up selector, and are just changing the bit depth within ColourSpace.
So that is then back to my original comment.
Seems like your 10 bit workflow is invalid in some way.
But it is not a ColourSpace bug.
And just to be totally sure, I have just tested PGen with a 10 bit monitor here, and as excepted all work totally correctly.
Steve
Steve Shaw
Mob Boss at Light Illusion