It moved 0.6 of an inch. Even a small amount like that is sufficient for it to feel wrong.
I've just tried locking/unlocking the car several times, but the seat didn't move, so I'm counting that out, partly because it's crept forward in the past without me locking/unlocking the car a lot. I'm starting to think that the seat switch might be faulty, making an occasional contact somehow.
I've started making a time/date/movement chart in Word
. Still got 2 years warranty and I know how Main Dealers like evidence!