Invalid behaviour in assignments with maps on the left side

[zapateo]

package main

import "fmt"

func main() {
	m := map[int]int{0: 1}
	i := 0
	i, m[i] = 1, 2
	fmt.Println(m)
}

should print

map[0:2]

but prints

map[0:1 1:2]

Note: this issue may be related to #892.