It is very irritating, I want to give my sims all their own private space which also helps to ensure they only learn the skills I want them to learn, getting exclusive access to those items.
But I...
Ideas
As of the last update (or so) no locked doors work for household or non-household Sims. Everyone has free range. I've tried all types of combinations. I stopped inviting Sims in, chatting with them outside the house, only to have the Sims walk right in and do whatever they wished, including taking baths (with bathroom doors restricted to household only). Tested with mods removed/cleared cache/etc.
