Yes, we all regress in the presence of our parents and siblings. One thing I have noticed both in myself and my bride is that we spend years of working on aligning our habits and tendencies with each other with the goal of a more harmonious marriage. Then in the span of one plane flight we regress to our older habits driven by the influence of the family we grew up with.
Unfortunately for most of us, these little "quirks" often tend to drive the other spouse crazy. Some of this animosity, I'm willing to bet, ends up being transferred to the in-laws. I guess that's another way of saying "It's not my in-laws that drive me crazy, it's their habits!" Because those small things are amplified in a committed relationship.
As with all things, once this regression is observed it makes it easier to deal with. Both in myself and my bride. And my in-laws. That's why I write, so my observations become more organized and actionable. Because I'm task driven. Thanks to my parents….