What version of Go are you using (go version)?

I found this when upgrading from Go 1.3.3 to Go 1.5

What operating system and processor architecture are you using?

GOARCH="amd64"
GOOS="linux"

What did you do?

$ cat scango.go

package main

import "fmt"

func main() {
    var x int

    n, err := fmt.Sscanf("A", "%c", &x)
    println("n=", n, "x=", x, "err=", err)

    n, err = fmt.Sscanf(" A", "%c", &x)
    println("n=", n, "x=", x, "err=", err)

    n, err = fmt.Sscanf(" ", "%c", &x)
    println("n=", n, "x=", x, "err=", err)
}

What did you expect to see?

I expected what Go 1.3.3 did: it always gets the first character in the scanned string, either "A" or " ":
$ go run scango.go
n= 1 x= 65 err= (0x0,0x0)
n= 1 x= 32 err= (0x0,0x0)
n= 1 x= 32 err= (0x0,0x0)

That's also what my C compiler does
/* gcc version 4.8.4 (Ubuntu 4.8.4-2ubuntu1~14.04) */
$ cat scanc.c

#include <stdio.h>

main() {
  char x[33];
  int n = sscanf("A", "%c", x);
  printf("n=%d <%d>\n", n, *x);
  n = sscanf(" A", "%c", x);
  printf("n=%d <%d>\n", n, *x);
  n = sscanf(" ", "%c", x);
  printf("n=%d <%d>\n", n, *x);
}

$ gcc scanc.c
$ ./a.out
n=1 <65>
n=1 <32>
n=1 <32>

What did you see instead?

Under Go 1.5, it skips the blank, and advances to the "A" (in the second clause) or EOF (in the third clause):
$ go run scango.go
n= 1 x= 65 err= (0x0,0x0)
n= 1 x= 65 err= (0x0,0x0)
n= 0 x= 65 err= (0x7f555757b028,0xc82000a1d0)