weekdays header breaks when using localization

[remipou]

the header with week days shows wrong day when using swedish

 <ReactDatez
  value={this.state.createdDate}
  handleChange={this.handleDateChange}
  locale="sv"
  dateFormat="dddd DD MMMM"
  allowFuture={false}
  allowPast={true}
  yearJump={false}
  isRedux={false}
/>

see screenshots, with and without locale="sv" monday got "sö" (sunday in swedish) and so on... i tried to change the firstDayOfWeek prop but without effect