+1 on the possibility of infection, but...
Did you bottle from the keg, or did you split your batch between the keg and whatever didn't fit in the keg, you bottle-conditioned? If the latter, perhaps you provided a bit too much priming sugar in your bottles, which was not completely metabolized (leaving some residual sweetness, and maybe some diacetyl too)? If your keg was more highly carbonated than the bottles, that can throw of your taste perception of clean vs. sweet (at least, it does for me).