If I paste a tiff that is MinIsBlack onto a tiff that is MinIsWhite, the result will be an inversion of the tiff that is MinIsBlack.
The paste code should recognize the different photometric interpretations and match them prior to pasting.
Attached are two sample inputs and the result. Pasting black_minisblack.tiff onto white_miniswhite.tiff results in combined_miniswhite.tiff.
Version I am using is 3.15.1.