Hmm... Interesting. While your BTCGuild conspiracy theory is silly, you're right on the block. That would also agree more with my previous observations that the difficulty only seems to update after a block is found.
Something else happened in the time period you're talking about though. After block 326591 the difficulty updated. That was in the middle of that long block, so would explain the out of sequence update.
Alternately, why not just get all the data and look through it. Slush publishes all the data, so you can double check this all yourself if you want.
Yes, I could double check this data out for myself. I even go to Blockchain and look at every block found on days I decide to mine a little bit on ck.'s pool.
I probably burnt too much wood back in the day and it's made me paranoid of everything.