Shimano 105 shifters (especially fronts) have had a run of problems. I wouldn't be surprised to learn that your LBS guy called Shimano and had them send a replacement front shifter (my guy taught me to change the 9-speed ones without removing the handlebar tape, but I haven't tried it on the 10-speed stuff). Our shop dude said that the last two times he called Shimano about a 105 shifter, they didn't even wait for him to finish describing the problem before they issued a return number.