Same thing here. (I think I added a couple of cents to Nuthatch's discussion at the time - early June if I remember correctly).

My elbow was hurting like hell, especially when extended. Tendinitis was my doctor-friend diagnosis. Although according to the charts my stem was already too short, it obviously felt like that was the problem. I wanted to get an even shorter one but the LBS didn't have them on stock, so we ended up just turning the stem upside down so I gained about 1 cm, certainly not more. No more elbow problem from that point! I am not as comfortable as I was when riding in the drops, though, and I feel that my thumb can get very slightly numb in the new position. So sometime in the next year I'll probably get that measured again and get a new stem.

Other suggestions: change position often, try and see if riding on the tops or in the drops make a difference... But DO fix the problem, it can lead to worse hands/elbows problems quite fast...