What steps will reproduce the problem?
Compile (8g), link (8l), and run this program:

package main
import (
  "fmt";
  "strconv"
)

func main() {
  var s1, s2 string;
  s1 = "a"+f1()+"b"+f1()+"c"+f1();
  fmt.Println(s1);
  s2 = "a" + f1();
  s2 += "b" + f1();
  s2 += "c" +  f1();
  fmt.Println(s2);
}

var count int = 0;
func f1() string {
  count++;
  fmt.Println("times f1() called =", count);
  return strconv.Itoa(count);
}

What is the expected output? What do you see instead?
Should be: 
times f1() called = 1
times f1() called = 2
times f1() called = 3
a1b2c3
times f1() called = 4
times f1() called = 5
times f1() called = 6
a4b5c6

Get:
times f1() called = 1
times f1() called = 2
times f1() called = 3
a3b2c1
times f1() called = 4
times f1() called = 5
times f1() called = 6
a4b5c6

Looking at the assembly output, you can see that the function, f1(), is
called left-to-right three times and the results pushed on the stack. Then
the results are popped off the stack and concatenated to form string s1,
making it look like f1() was called right-to-left.

What is your $GOOS?  $GOARCH?
linux, 386

Which revision are you using?  (hg identify)
47a7d31e4405+ tip

Please provide any additional information below.

This example program is based on the discussion on the golang-nuts group
called "String concatenation evaluates Right to Left, not Left to Right."
started by ray (r...@hollett.demon.co.uk) Dec. 1st.