The bug exists, I know that from watching a friend enter his own house and the demo timer not resetting (my character was a tenant so I could verify through my own timers).
What triggers the bug? Haven't the faintest idea.
We could have fun dreaming up explanations such as they've got some dumb coding that registers house entry between 12:01pm JCT and 12:00pm JCT but not between 12:00 and 12:01pm, and those affected have been those who finally got around to entering during that single minute of the day. Unless enough players who only enter their house once every couple of weeks get into the habit of checking their estate timers (or system messages in chat) to make sure it's not showing active for demolition and catch the failure to reset so it can be reported with specifics, the bug will never be acknowledged by SE or the cause determined.
If you're going into your house regularly, there shouldn't be anything to worry about. Even if your entrance isn't registered on one occasion, the timer will no doubt reset the next time you walk in.
It's those who rarely go into their house that need to be cautious.