Rails improperly pluralizes the word "penis". From the New Oxford American Dictionary:
penis |ˈpēnis|
noun ( pl. -nises or -nes |-nēz|)
the male genital organ of higher vertebrates, carrying the duct for the transfer of sperm during copulation. In humans and most other mammals, it consists largely of erectile tissue and serves also for the elimination of urine.
As described here, there are two appropriate pluralizations of the word penis: penises or penes. The more common pluralization, penises, should be used.
While technically this is a defect, "enhancement" feels like a more appropriate word to describe this particular problem.