I discovered that one of the issues with the pesky Front Door was caused by having two mailboxes. I have yet to find how the extra mailbox gets created. The front door is still flawed without a doubt.

I discovered that stepping through objects with Set to Next is not done in growing order from lowest to highest, as one might intuitively expect, but roughly in their order of creation. After all the years I didn't know this. But sometimes the order is different as in the case of the mysterious copy of the mailbox that was found first.

Here on this lot the correct mailbox has id 2, and the copy was created recently with id of 1114. Then I made a few more. Then I freed up id 125 by deleting some bushes, and created another one. They were found in order of 1114 -> 2 -> 1135 -> 1136 -> 1137 -> 125.

After deleting all the extra mailboxes the food deliverator finds the correct front door instead of the back door, which was closest to the second mailbox.

The right thing to do when selecting the refobject is to check that it is in room > -1 (at least).

The MailBox seems to be immune to Remove Object Instance. Nothing happens. How bizarre. I can only delete it by grabbing and selling it.