The Dominant trait does not appear to have been removed due to malfunctioning code, rather it was likely reworked as a birth trait rather than a trainable trait. Mav preferred to hoard old code rather than lose his previous work. (Edit: This hoarding is a bit less obvious now than it was a couple versions ago as I have deleted several of his hoards as I reworked various files, though I have created some new hoards as well.) The game has been reworked many times over the years.