I've been driving standard for 10 years, and only once have money shifted. (Down to 2nd instead of 4th)
I noticed something was wrong, and clutched in only to release the clutch again a second later.
Watching the video later on, I figured out what happened.
My seatback is malfunctioning and I sit slightly twisted. I was subconsciously adjusting myself in the seat almost every lap on the straight to make up for this. This time I didn't and it put my arm at an awkward angle, so I grabbed 2nd instead of 4th.
Thank god I had just adjusted the valves about a week earlier, and that my engine has lived an easy life behind an auto box (before I swapped it). Usually ~8000rpm on an M20b25 is bending valves.
This happened at the beginning of the track evening, and the motor ran strong for the rest of the night, so no harm done.
I've pulled the driver's seat, and the plan is to fix the seatback issue (along with the houndstooth cloth) some time before the spring.