The motor will usually have a little sensor to know the position of the wipers when parked, it may be the sensor is playing up or the wipes just miss the parked position so next time you start the car it parks them again when it checks everything on start up.
I’d check the scuttle for water and dirt, it may be you’d need to replace the wiper motor to fix it, but if everything is working otherwise then I’d just put up with it