According to Shimano, the Ultegra 6700 RD is not compatible with the 12-30T cassette. As I wrote yesterday, I got mine to work, but to get the shift quality that I wanted, I had to spend a lot of time and set the B screw about halfway of travel.

I may put the Tiagra 4600 RD back on the bike if it gives me any more grief in the future.