Double vision converging back to single

I noticed today on a number of occasions when I looked at a car dashboard button with a high contrast label (white text ‘POWER’ on black button) I saw a doubled text image with about 1 centimetre of separation slightly offset from the vertical. If I focussed on this (car was parked), the higher image would start to move back towards the other over two to three seconds, until they both synchronised to a single image. I have had double vision and ghosting before but never observed double images converge back to a single image. Anybody else experience this?