If you immediately u-turn after countdown text, then the “you are going backwards” text doesn’t appear. You can complete whole laps backwards without it appearing.
Are you having any issues where “backup” is suddenly being triggered? Where, like, you’re driving forward–maybe even with a boost or on a boost pad and suddenly your MPG goes to 0 then you move backwards? I’ve had it happen on both an X-Box controller (with and without keyboard being plugged in) and keyboard (without controller being connected).
Haven’t had it happen, was just messing around with accelerate and found this.