I recently purchased a K2 Mod 5.0 frame and fork. The bike was built by a mechanic at my local bike shop. The components are mostly Ultegra but with a Dura-Ace rear derailleur, 105 hubs, BB, and crank. The chain is a SRAM PC-69 and the cassette is a Shimano CS HG-70.9. I have suffered ghost shifting every time I've gone for a ride, but after about 10 miles of riding. Before the 10 miles, everything works fine.
A mechanic at the bike shop replaced the rear derailleur cable. A second mechanic insists the problem is cable stretch and has adjusted the rear derailleur several times. All to no avail. Yesterday, I insisted on replacing the rear cable housing, the one from the chain stay to the derailleur, with a longer housing. The original housing was about 10 1/2" and the replacement is about 12". With the replaced housing, the ghost shifting started up again after about 10 miles and got progressively worse. I turned the barrel adjuster a quarter turn clockwise once the ghosting began. I made this adjustment several times. After one complete turn, it seemed the problem was solved. At least for a couple of miles. The ghosting returned.
The bike has less than 100 miles and other than the shifting problem, this is the best bike I've ever ridden.