Nightly is totally unstable. Features get added, and might get removed if the team decides they're not a good idea. So programs that want to use such an experimental feature might only work for a certain few versions of Nightly, because Nightly only guarantees the stability of features that have been released to Stable.

That's why it's strongly recommended not to use Nightly to write your programs: they'll almost certainly break, and since Nightly gets released every 24 hours they might break daily. If you don't have the time to fix things every day, you shouldn't be using the unstable features!