0) Ensure you use sysetem file/folder picker [Tools->Options->General]
1) Execute following Basic script, in the folder picker dialog enter an HTTP URL
(e.g. http://www.blahblah.com) and hit Enter

  oFolderPicker = createUnoService( "com.sun.star.ui.dialogs.FolderPicker" )
  oFolderPicker.DisplayDirectory = "file:///d:/source"
  if ( oFolderPicker.execute = 1 ) then
    msgBox oFolderPicker.DisplayDirectory
  else
    msgbox "FolderPicker cancelled!"
  endif

=> Dialog disappears, oFolderPicker.DisplayDirectory contains
'file:///d:/source' and not the URL just entered!

===> The dialog should refuese to accept things it cannot handle.