It's documented behavior in [MemoryManagement.md](https://github.com/ReactiveCocoa/ReactiveCocoa/blob/83fd4ad0f3e7e291c2fc93e9dff5565cf1ccd67c/Documentation/MemoryManagement.md), see the very end.

Even if not well known, people may still depend on it, and, 3.0 is the future so why force it here?