http://keiwando.com/evolution/faq/glitch-fix/ has a rough explanation why I haven't "fixed" this issue, which is essentially a continuation of http://keiwando.com/evolution/faq/glitch/ (I know that you're not focused on the fact that you can reach 100% fitness with this bug, which is the main focus of the second link, but it's the same issue and a setup for the FAQ of the first link)