It really does!
Duplex gene (D^v) does mimic a buttercup comb when heterozygous and no other comb genes are at play, but the buttercup comb is actually a different allele of the same gene (D^b). Heterozygous duplex would make some single combs and some v-combs if two birds with that type of comb were bred together, whereas you'll always only get buttercup combs when breeding buttercup combed birds together.
