I was on a ride Sunday and that same thing happened to me only with the rear shifter. It wants to jump back and forth between two gears. At one of the sag wagon stops they looked at it and said it is in the shifter, a part called the pall(sp) is broken. They said I could nurse it and finish the ride, so I did. But they told me that it would have to be replaced. I happened to have a two chainring, 8 speed Shimano 600 Ultegra setup and they thought the only viable replacement shifter was a Sora, since that was the only 8 speed they thought Shimano made. I have since heard there might be a Shimano R500 (not sure of the number) that is the same styple as what I have. So I hope that helps. I might ask the and add to your thread this question. Is it fairly easy to buy and install the shifter yourself? I was in kind of a hurry to get back out again and hoped I could grab one, install it and go before the LBS could fit me in.