If I have constructed my tree correctly (and I believe this part is accurate), I have discovered that my mother and father share a common set of great+ grandparents. On my father's maternal side, this couple is 13th generation. On my mother's maternal side, this same couple is 14th generation. The son of these two continued my mother's line, and his sister continued my father's line.
I am new to researching ancestors, so I'm wondering if more experienced members have encountered this phenomenon before.
So, any guesses on how often this sort of thing occurs?