The first time I did STS the same thing happened to me, I put on muscle, but sure did put on what seemed like fat. Within a month it seemed to disappear. My next round of STS, about 3mo later, l definitely saw amazing results, no weight gain, and great definition. I was also trying to fit in cardio on those days, the second time around I did not do cardio, lesson learned!
That is encouraging to hear. May I ask when you did do cardio what type was it and how many days a week?