readf error bug?

[Dave Akers via Digitalmars-d]

The following...

import std.stdio;

void main() {
	write("How many students are there? ");
	int studentCount;
	readf("%s", &studentCount);
	write("How many teachers are there? ");
	int teacherCount;
	readf("%s", &teacherCount);

	writefln("Got it: there are %d students.", studentCount);
	writefln("And there are %d teachers.", teacherCount);
}


When given the input...
10
42

will produce the error...
std.conv.ConvException@/usr/include/dlang/dmd/std/conv.d(2013): 
Unexpected '4' when converting from type LockingTextReader to type int

I understand what is wrong and how to fix it but the produced error is 
incorrect.