I found a very special blueprint hierarchy where a publication has two parents, being one of them parent of the other. Here is a graphic representation of what I am talking about:
I had never seen something like this and I am thinking of possible scenarios where this make sense, so calling for all those Business Analysts and Functional Consultants to give it a thought and share with me.
Additional Information: This publications are all content publications, and are not used for a multi-language situation. In fact the website is in English-only and has no blueprint design for multi-language.