it definitely isn't the door. i made the door myself (rather, completely changed an existing default door) and it has worked perfectly several times previously, and in fact, after remaking the curtain system as per what i wrote above, it worked just fine. it all seems pretty weird to me, but there it is. seems like either it shouldn't allow you to make an upside down curtain system, or it should at least allow you to flip it after you've finished..