Yes, it is quite common, but not typical. I was trying to draw a distinction between the issues that poly/poly relationships (which I call typical poly) have, and those that mono/poly face, which I think those that have only been in poly/poly relationships aren't going to know about.
Because it's not about cheating. The main issues are the things I mentioned before, which I won't repeat.
"Listen, or your tongue will make you deaf." - Native American Proverb