Funkce pro míchání kanálů ve Photoshop už delší dobu nefunguje správně. Potřebuji ve formátu CMYK dát obrázek do kanálu černé barvy a je to příšerný problém.

I am not using the Beta version.

Thanks for the videos. 

They seem to be missing the UI elements you are manipulating, though, strangely enough. 

Are you applying the Adjustment destructively? 

If so I would recommend using a Clipping Masked Adjustment Layer instead. 

And unless you have a preferred mixture of the four process colors to arrive at your grayscale I wonder if Hue/Saturation Adjustment layer might not serve just as well. (see screenshots)

I'm sorry, but I'm very busy with work, and I don't know how to film the video and I need to do a lot of work now. If you try to convert a color image in CMYK format by mixing channels, for example, to the black channel, you will immediately understand how badly Photoshop works. The problem is obvious to anyone who needs to use this function. I need black to be really black in print only in grayscale, but I need the other elements in the file to be colored. I'm not solving anything else, just the malfunctioning of the program. I need Photoshop to finally be fixed and this function to work properly.