A note on rendering with levels

Writing this down in case it helps someone else. (I just lost a couple days of render to it.)

The [video, full] levels do not work the same with the "retain sub-black and super-white data".

Long story short, you want video levels and the "retain" checked, if you want that data preserved. Otherwise you will clip it in the render.

In other words, that "retain" check box doesn't work with "full" levels. Possibly a bug, not sure what behavior they'd otherwise be going for.

This as I would expect. Full levels do not have any data below 0 or above 1023. As 0 = black, sub-black would have to be below 0, which cannot exist. Super white would have to be above 1023, which also cannot exist.
Video levels have black at 64 and white at 940 (Y) and 960 (UV colour difference signals). This allows for sub-black and super-white.