I agree that this shouldn't be happening, but it does sort of match the Gear Position Control description on page 127
Specifically:
Operating the shifting switch does not shift the front derailleur.
Instead, the rear derailleur is shifted down through two gears
Now... you do not need a new battery in order to "use" Gear Position Control, but I always thought you needed both derailleurs to be r8050 or r9150. Apparently that is not the case.
Whether or not GPC is enabled / can be switched off depends on the selected chainring/cassette, as you've already found out ;-).
BetterShifting.com - Di2 help and guides| BetterShifting Instagram | Terry's Instagram
Specifically:
Quote:
When the chain is in the range [1], shown in the illustration. Operating the shifting switch does not shift the front derailleur.
Instead, the rear derailleur is shifted down through two gears
Now... you do not need a new battery in order to "use" Gear Position Control, but I always thought you needed both derailleurs to be r8050 or r9150. Apparently that is not the case.
Whether or not GPC is enabled / can be switched off depends on the selected chainring/cassette, as you've already found out ;-).
BetterShifting.com - Di2 help and guides| BetterShifting Instagram | Terry's Instagram