Cautionary coloration

[annplaksin]

It seems, at least in sources, that something like "cautionary colouration" can happen, e.g. in this tenor of the M. Ave Maris Stella in Jena 3:

Comparing this to the Petrucci version (which seems somehow messy but has a dot of division between the two semibreves), it does not make sense to shorten the black semibreves, while the black breves indicate imperfection.

It needs to be checked with the formalization of rules and Tinctoris' writings.