At BTC Guild's current shift length and the network difficulty, the AVERAGE blocks for a shift (once closed) is between 10 and 11.  This means if the pool has a really long block, you can see 5-8 of the most recent open shifts with 0 blocks.

Right now we're at a little under 6 hours without a block.  Not exactly hard to believe, that's only ~6x difficulty, something which happens at least once a month (probably more).