Originally Posted by
FBinNY
If yes, than odds are that either the cable head is slowly coming off, or pulling through the lever cam, or the housing is extruding through a ferrule, or at the lever. The other related possibility is that you didn't properly seat the housing in the lever before taping your bars, and the housing is slowly creeping forward toward the lever, effectively getting shorter.
This is a classic "raise the bridge or lower the water" scenario. Either the wire is getting longer, or the housing shorter, and a bit of tracking down will verify which and where.
Check your cable housing ends too. If you see a tiny wire or two sticking out - that's it. Pull off the cable housing end, cut the housing so it's square, put everything beck together and you'll be good-to-go.