That's very interesting, I had never realised before that a good DJ should not only take into account the beat of the tunes being mixed but also the key. A badly chosen bassline could make a terrible harmonic mess of two good tunes.
Dm is the relative minor of F major, the only different note from Cmajor is bB vs B, maybe the Dm mix fits better with a Fmaj tune, it all depends on the chord progressions used and to what chords they're resolving.
Interesting. C major and A minor are relative keys and are about the same, same scales, same chords, so I was expecting that the software would get them mixed, which it seems it did. I don't know what to do with the D minor one, Is that remixed way more altered than the other ones?