parse slice map to map got wired result

[timestee]

sm: 
  - foo : bar
  - bar : baz

type Conf struct {
   Result   map[string]string `xconf:"sm"`
}

got this result：

map[string]string{"bar" : "baz"} 

it should be:

 map[string]string{"foo": "bar", "bar": "baz"}