Our coach has an automatic Fantastic in the bedroom and a manual one in the living area. Bedroom one had annoying habits similar to what you describe. I made it "manual" by disconnecting and taping a motor wire and putting a couple 5/16" lockwashers over the knob shaft so it couldn't be pushed to engage the motor gears. We have MaxxAir2 vent covers so I don't care about the auto-close feature. MUCH happier with the vent.
I think the cover motor was confusing, or confused by, the position of the cover. It seemed worse when the house battery had been disconnected and reconnected.