sour is definitely not a characteristic of this yeast and most likely there is something else going on:
SOUR-ACIDIC
CHARACTERISTICS: Another of the basic tastes. This is perceived on the sides of the tongue towards the back of the mouth. At higher levels it can be felt all the way down the throat. Generally in beer this is perceived as a sour aroma and a tartness or vinegarlike aroma. Bacteria contamination sourness can also be perceived as spoilage or putrefaction.
CHEMISTRY: Caused by lactobacillus, pediococcus, acetobacter and some yeast strains.
HIGH CONTENT DUE TO PROCESS: Poor sanitization; bad yeast strain; too much corn sugar; excessive amounts of citric or ascorbic acid; high fermentation temperatures; excessive acid rest; mashing too long; use of wooden spoon in cooled wort or fermentation; storage at warm temperatures; scratched plastic fermenter.
LOW CONTENT DUE TO PROCESS: Good sanitization; stainless steel equipment and spoons; cool fermentation temperatures; cool beer storage; mashing for not more than two hours; glass carboy fermenter