The other thing in terms of randomness... I recall that oddly enough, clumping is a sign of randomness rather than a sign against it. That is, in a truly random sample, it is far more likely that multiple similar units will clump together than it is that they'll be spread proportionally through the deck. If you think about this, it makes sense - statistics works only when applied over a massive number of iterations, after all. I'm not mathematically minded enough to try and give a full example, but it's probably not as surprising as it seems at first glance...