Hmm, is this really such a problem?
Killing your teammate arguably shouldn't be rewarded, but even then it might be part of a bigger team strategy that your partner has consented to.
If you want to kill your own units, why not let it level you up? (And are elite horsemen really as strong as it sounds? Damnit, I might have to go back to Tech?!)
If I recall correctly, you can level up by killing your own units in Warcraft as well, but of course that doesn't mean it must be in Glest. Just saying it's not really abnormal. Anyway, it has apparently already been removed, so yeah. Probably not a big deal.
~~Djemynai