I recently built a new building in a village my started, i used iron doors so villagers can't open and close the building, i was building it and i installed a way to open and close the iron doors, i made sure to turn it on, so the doors stay opened, then when i wasn't paying attention the door closed, i got confused because the the door should be opened, i was watching carefully and i saw that my villagers were going into the building and closed the iron door(they couldn't open it though) i was sure this was a bug.

The best way to recreate it is probably just to replace a door in a building that the villagers would go to,then replace it with an iron door and leave it open, as soon as they go in or out they would close the door