Front derailleur trim issue
I have an Ultegra 9-speed set up with a compact double crank. The bike rides and shifts flawlessly except for one annoying issue, which I need some insight about.
The left shifter has 4 positions and I have them set up in order as follows - #1 small chainring, #2 small chainring trim, #3 large chainring, #4 large chainring trim.
When moving through these positions in the order described, the shifter and derailleur work perfectly. However, when I'm in position #4 or #3 and try to index down one position, the shifter always "dumps" me all the way back to position #1.
I'm stumped...adjusting cable tension doesn't seem to solve anything, the shifter has been lubed and works fine for all other functions, the cable seems to be running smooth and not hanging up.
This issue exists when riding and also on a bike stand.
Can anyone suggest to me what might be happening? Thanks