PBS seems to have this pattern that they follow 90% of the time: six to eight weeks of episodes from Seasons Nine to present, and maybe a week of episodes from the first eight (two weeks, if we're lucky)... then, the other 10% of the time, they'll alternate every other day for a couple of weeks.
While I do find it very annoying, irritating, and bothersome, I have to disagree with you on Season Eight CD, that's one of my favorite (I know, everybody is always shocked when I say that).