Nano's new maintainer (Benno) didn't like GNU's maintainer agreement and refused to assign copyright of his contributions to the FSF. So instead he forked the project to maintain it ouside of GNU.
Which has been mostly okay with widely-distributed ownership, but was a problem in Christoph Hellwig's case against VMware recently. So there's an actual problem of enforceability, versus the project-hampering PITA factor of CLAs at all, e.g.https://lwn.net/Articles/443989/ It's a seriously tricky balance issue.
HN discussion from two months ago: https://news.ycombinator.com/item?id=11953044