Yeah, it's a bit of a mess.

Bitcoin protocol has allowed people whose clocks disagree by up to two hours to participate in the network.  I suppose the idea may have been something to do with clocks disagreeing until people reset them at daylight saving time transitions.

And some folks have tried to take advantage of that one way and another -- I think that at one time it may have been advantageous for miners to have their clocks set differently from the rest of the network or something a bit crazy like that.

So, yes, you're going to get a few later blocks that are timestamped earlier than the blocks they come after.  It didn't really happen that way of course; it just looks like it because some of the people had their clocks set wrong.

Personally I think that was a mistake.  If someone can't be bothered to keep her computer's clock set right, then kick her off the network.