You know, I can kind of understand the people who don't realize they can't affiliate with two different sororities on two different campuses. (Although I remember it being covered during our new member ed.)
On our campus though we had a slightly different situation. A girl transferred in and was a member of ABC at her original school. We had a chapter of ABC on our campus, but they were not a particularly popular sorority so this girl went through rush and joined XYZ instead. She was initiated and even moved into the house winter term. She was eventually found out though. Apparently she talked about ABC a little too much (including ritual) and one of XYZ's field consultants got suspicious.