title: Default file type in tkFileDialog's askopenfilename method
body: <p>For some reason, the default file type changes depending on whether I open the file dialog with the menu, or withe the Ctrl+O hotkey.
  Why?</p>
  
  <pre><code>from Tkinter import *
  import tkFileDialog
  
  FILEOPENOPTIONS = dict(defaultextension='.bin',
                         filetypes=[('Bin file','*.bin'), ('All files','*.*')])
  
  class TestGUI(Tk):
      def __init__(self):
          Tk.__init__(self)
          self.title('Test')
          menu = self.menubar = Menu(self)
          fmenu = self.filemenu = Menu(menu, tearoff=0)
          menu.add_cascade(label='File', underline=0, menu=fmenu)
          fmenu.add_command(label="Open", underline=0,
                            accelerator='Ctrl+O',
                            command=self.fopendialog)
          self.config(menu=menu)
          self.bind_all('&lt;Control-o&gt;', self.fopendialog)
  
      def fopendialog(self, event=None):
          print repr(tkFileDialog.askopenfilename(parent=self,
                                                  **FILEOPENOPTIONS))
  
  if __name__ == "__main__":
      test = TestGUI()
      test.mainloop()
  </code></pre>