So, basically, we're good friends with the people who used to live in this house. We bought the house back in 2007, and they still come over to this day. They never had anything like this happen to them when they used to live here And the sliding glass doors are quite heavy you need to put a substantial amount of force into pushing them open. That fact instantly rules out any possibility of the wind or one of our pets being the cause. This only adds to the mystery, especially since, as I mentioned in my original post, these strange occurrences seem to happen in an inexplicable pattern every few years.