Beep using date picker

Using a date picker (from the examples) in an OS X desktop app, when the calendar window closes and focus is returned to the textedit representing the date, I receive a beep. I am assuming the beep is trying to telling me there is something wrong. Is this the case? Not sure how to troubleshoot or stop the beep from occurring.

code behind button calling the calendar window

  //Use Calendar Window to let user pick new value for myDate
  myDate.totalSeconds = Calendar.GetDate(myDate)
  myDateField.text = myDate.ShortDate

After updating the window type from document to movable modal, it no longer beeps. Not sure what that’s all about.

Same problem here - Modal Dialog creates beep on closing, changed it to Plain Box - now works.