Composer to split

there are 3 track double composers “Goran Bergovic / Iggy Pop” that should be split in the 2 artist. (in my tags they are splitted, so they appear also as separate composers…)
if i try to edit the 3 tracks/compositions (to remove the double one), anyway, i get:

so… the double artist is missing.
in the composition screen, though

this is part of a general problem: composition composers are different from the displayed track composers, and do not take into account the file tag composers.