One member of the FC i'm in had some sort of fight with its former Leader and she left...joined the FC that I am in and after sometime she sorted out the dispute and just said that she is welcomed to the FC again so "Thank you and bye bye". I am sorry but this is not alright, for the most part this FC help't her out with end-game content and as you know sometimes you pause your own activities in order to lend a helping hand. Changing FC's is not unavoidable, I always chose the clan carefully before joining and chat with the leader about their goals and unless things become really, really bad I will always stick with my choice, because a person that changes clans at an alarming rate cannot be trusted.