Are you using Star San as your sanitizer? Star San is darn near useless against wild and domestic yeast, which is why it should not be promoted as a do-all brewing sanitizer. You need to use an oxidizing halogen to kill wild yeast, which means diluted chlorine bleach, iodophor, or peracetic acid. Most wild yeast are POF+, which yields the Belginesque flavors. I waged the same war until I read up on Star San. Star San is more accurately a bacteria killer. Star San is only attracted to positively charged cells because the killing agent, the surfactant known as dodecylbenzenesulfonic acid (phosphoric acid just lowers the pH, making the surfactant more effective), carries a positive charge. Yeast cells carry an negative charge; therefore, they repel dodecylbenzenesulfonic acid. If you are using Star San, throw it away and purchase a bottle of iodophor and learn how to use it without leaving stains all over the place. You will thank me later.
By the way, you are more than likely picking up the wild yeast on the initial pitch. Wild yeasts are not as strong multipliers as domesticated yeasts, but every repitch cycle gives them a chance to multiply. Successive repitches can result in the cell count being high enough for their metabolic waste products to get about taste threshold.