Single tap AutoSteer incorporates TACC as part of Autopilot. The problem then is when a lane change occurs during AutoSteer, the Autosteer cancels together with TACC causing the car to automatically slows down (regen braking) as there is no pressure on accelerator. (At least that's my intepretation)when you have single-tap-Autopilot enabled, TACC-only just doesn't exist
A double TAP Autosteer reverts to TACC after a lane change is forced or steering wheel is taken over by driver.
Its almost as though Elon is trying to