Image masks as CMYK but not CMYK in preflighting

I have a question about the preflighting in Acrobat.

I have a control profile to check that the PDFs are printable (so it checks for the presence of an inking rate higher than 300%, a CMYK profile, images higher than 150 dpi).

When I check some PDFs, it indicates non CMYK images but in detail they are image masks that are well marked as CMYK.
This happens especially when exporting from indesign with the profile.
Why does the upstream control indicate that these elements are not in CMYK when they are?