I have the same problem going on right now! I used wyeast's French Saison yeast in a rye Saison, then my next batch in the keg (a scotch ale) now tastes like a Saison? I let everything soak in oxyclean for a few hours, rinsed, then soaked in Starsan for about an hour. Keg lines and seals are relatively new... Such a pain! I already have dedicated sour keg lines, and to top it all off I have a Saison in another keg right now too!?!?!
Primary - Wit, Lambic 1
Secondary - Berliner Weisse Experiments
Keg - Berliner Weisse, Lemon Lime Hef, Arrogant Bastard Clone
Bottled - Lots
Up Next - Rye Saison, Pumpkin Ale, Citra IIPA, Rauchbier