title: Styled WPF DatePicker loses format on focus loss, regains on programmatic update
body: <p>I've an oddity with the WPF DatePicker that I've demonstrated in a project downloadable from <a href="http://dl.dropbox.com/u/25030054/DatePickerIssue.zip" rel="nofollow">here.</a></p>
  
  <p>I need a datepicker styled to look like normal text, with no button or outline, to pop up the calendar when a seperate button's pressed, to let the user edit the text, and to show the date in the format we want- dd MMM yyyy. </p>
  
  <p>What I have almost works, but when losing focus the date format reverts either dd/mm/yyyy or mm/dd/yyyy, alternating each time focus is lost (i.e. clicking on the date and tabbing out without editing), until the control is next updated completely independently from code, which pressing "Rewrite" does.</p>
  
  <p>Can anyone shed some light on what's going on and how to fix it?</p>