Powershift upshifting on its own if you hit a bump hard enough?

[Veloo]

Just at the LBS and talking to one of the staff there that had 11 speed silver Centaur on his bike.
He said on more than one occasion, he'd hit a bump on the road hard enough that his drivetrain would end up going up a gear (smaller cog). He pointed the finger at the Powershift lever.

I've ridden Powershift Athena 11 for a bit but have never had that happen to me. Never had it happen on my current Ultrashift either.

Anyone here ever experience it themselves or hear about it?