Good. I'm so happy they put it there. It's a little thing, but such little things - documenting corner cases - can have great benefits.

I have a bad memory for all but most frequently used standard library calls, so I regularly end up refreshing my memory from cppreference.com, and I tend to instinctively scan any notes/remarks sections, as there's often critical information there. So now I can be sure I'll be reminded of this the next time I need to use scanf family.