IL-27 is a cytokine that is a protein complex composed of two subunits, the IL-27p28 subunit (the product of the IL27 gene, considered the alpha subunit of IL-27) and the EBI3 subunit (a product of the EBI3 gene, the beta subunit). When we say IL-27 biosynthetic process in the GO, we mean the biosynthetic process that results in the complex, meaning biosynthesis of the entire protein complex, meaning of both subunits and their association. And we are _not_ talking about IL-17D, which is a separate cytokine entirely that was briefly named IL-27 before the nomenclature got sorted out (everyone wants to call their new cytokine an interleukin -- it's got a bit of cachet, although it's essentially meaningless in terms of structure, function, origin, or target). GO should therefore not have the "intersection_of: OBO_REL:results_in_formation_of PRO:000001141 ! interleukin-17D" statement at all. Perhaps you need to provide two intersection_of statements referencing the two protein subunits of IL-27 to form the logical definition for the GO term.
IL-12, IL-23, IL-35 are three other cytokines made up of two subunits. The first two also have GO biosynthesis terms that need to be dealt with in a similar manner. The third is relatively new and the GO has not caught up with it yet.