PL7 Elite: Black & White channel mixer not working

[platypus (Canon & Mac (Intel and M1))]

@KameraD

Can only say, works for me. iMac Intel, 13.6. PL7/FP7.

Yes, with FilmPack, the tool works.
This issue is with DPL without FilmPack.

Meanwhile, we can always use the HSL tool for B&W as shown below (with a slight variation)