iTunes shuffle by album

I think Matt may have mentioned this to me earlier, but iTunes is really annoying me right now:
When I try to shuffle a particular playlist by album, some of the albums break up all over the place while others stay together. And it's not just a matter of whether the whole album is present or not. I can't figure out what the difference is between the ones that stay together and the ones that don't, either. It also seems to always be the same albums that break up and stay together, too...
Ideas?

集中能力無し

集中できねぇよ、全然。この作文書かないといけないのに．．．