The 7th Domina's dialogue you get for asking who is next is what I was talking about. You are supposed to go through the white door to get the option to submit to them and if you don't submit it gets locked. I am guessing since you left the room with the door, it locked because it is supposed to lock when you re enter the room without submiting. It's an odd issue with the codeing that I guess was an oversight. Dekarous might fix it but it would probably cause issues for those that already did interact with them in the room behind that door. Codeing can be rough since if you don't expect every possible thing a player will do, something will go wrong. Though I personally enjoy codeing despite it's challenges.