[pinterf]

Thanks, that gamma thing found, classic avs is ok, for couriousity I'll check when it disappeared.

EDIT:
nothing has been disappeared.

The biggest difference I found is that in AVS+ the "PC->TV" and "TV->PC" conversion happens at the end of the gain-contrast-offset-gamma conversion, while classic Avisynth is doing that the the beginning of the process.

There is no correction before applying gamma in either versions. Assumes PC range.
This is why it worked for you with an input having PC levels.

Now when you want to have proper black levels you have to do similar like this:
ColorYUV(levels="TV->PC").ColorYUV(....,gamma_y=-40).ColorYUV(levels="PC->TV")
Which is obviously not a nice solution.

In theory, the ColorYUV function (after modification) would know that it should apply gamma on TV level.
We surely know that input is PC or TV range when levels="TV->PC" or "PC->TV" is given.
When none of the above levels parameters exist, coring=true would also indicate that the clip is TV range.

Probably levels="TV" (a newly allowed value for "levels") would help clarifying if none of the above mentioned options are set. (Why cannot we have frame properties in avs?)