Map type cause error "already set in map" with ErrorOnUnmatchedKeys, multiple YAML overlays

[xmlking]

I am using following structs and enabled ErrorOnUnmatchedKeys

Got Error
yaml: unmarshal errors:\n line 21: key \"account\" already set in map\n line 24: key \"greeter\" already set in map\n line 27: key \"emailer\" already set in map\n line 30: key \"recorder\" already set in map

type Service struct {
	Endpoint             string   `yaml:"endpoint,omitempty"`
	Version              string   `yaml:"version,omitempty" default:"v0.1.0"`
	Deadline             uint32   `yaml:",omitempty" default:"1000000"`
}

type Configuration struct {
	Services             map[string]*Service   
}

config.yaml

services:
  account:
    endpoint: mkit.service.account
    version: v0.1.0
  greeter:
    endpoint: mkit.service.greeter
    version: v0.1.0
  emailer:
    endpoint: mkit.service.emailer
    version: v0.1.0
  recorder:
    endpoint: mkit.service.recorder
    version: v0.1.0

config.development.yaml

services:
  account:
    endpoint: mkit.service.account
    version: v0.2.0
  greeter:
    endpoint: mkit.service.greeter
    version: v0.2.0