You have a v3, right? I think I saw that in one of your other posts.
Anyway, as you know, when you download, you start off at the last major event. I suppose the only logical explanation for this glitch is that it somehow skipped not only back to the last major event, but back to the last generation, when you downloaded. The only reason this is even remotely half-way plausible is because the parents and grandparents are stored in the family book -- perhaps it reverted to the mimitchi you had before, thinking for some reason that the evolution into mimi was the last major event or something? Very odd; I really don't know.
