If you find yourself repeatedly adjusting the cable tension, check all of your cable stops. Sometimes the cable housing tries to shorten itself. What you are looking for is one or more of the tiny cable housing wires sticking out.

Just for my own information, how do you like that low-normal derailleur? I absolutely despise the C-101 and C-201 stuff, but I don't have any experience at all with the better quality low-normal components.