I'm not sure, Dagmar— it seems to be a scattering of seasons sometimes. Last week I watched an episode in which Booth had brain surgery, but this week there is no mention of it and Booth looks fine!
Yeah, we have the same here.. Yesterday we've had an episode from season 4, today season 6.. sometimes we have 3 episodes in a row and first episode is season 6, then 3 and then 4.. it's really funny :-D