If you look, Bonderman fades late in the season (or he has the last two years):
The theory is that his power-pitcher repertoire starts to fail him as he tires late in the year.
Whatever it is, it seems to only impact his BB rates:
His K-rate seems to hold just steady throughout the year.
I traded 3 years of Bonderman for a year of Haren and Beckett a few weeks ago, and I don't think I'll regret it one bit until next April.