You don't need the spec to see that "0xz" doesn't match "%x%c". The man page for scanf is sufficient, as is having read K&R. This is extremely basic C standard library stuff; it's not an odd corner case.
Sure. A good maintainer would see that, and perhaps ask politely for the missing required information.
That's the main job of a good open source maintainer really. Asking for people to provide more information, test cases, and documentation.
In this case, the maintainer queried the behaviour (in a rude way granted), and was not sure why it was wrong. All that attitude from the maintainer was definitely not needed.
If someone reports a bug to your project, make them feel welcome! Numerous times, I've seen these single bug reporter people turn into long time contributors. All it takes is a bit of attention, giving them credit, and providing a nice environment for them.
Anyway, it's good there is a much more functional team heading glibc these days.
