title: Python 2.7/Windows: ttk combobox dropdown shows up underneath topmost root window
body: <p>I'm experimenting with the new ttk Tile enhancements that ship with Python 2.7. </p>
  
  <p>Windows 7: The code below demonstrates how the combobox dropdown shows up BEHIND our root window when the root window is configured as a topmost window ("always on top"). If you comment out the line """    root.attributes( '-topmost', 1 )""" then the combobox dropdown appears within the root window (as expected). </p>
  
  <p>Anyone have any workarounds for this behavior so we can use comboboxes with 'topmost' windows?</p>
  
  <pre><code># sample code that illustrates problem described above
  
  import Tkinter as tkinter
  import ttk
  
  root = tkinter.Tk()
  
  panelCombo = ttk.Frame( root )
  panelCombo.pack( side='top', fill='x', padx=12, pady=8 )
  valCombo = ( 'cat', 'dog', 'pig' )
  varCombo = tkinter.StringVar()
  varCombo.set( 'fish' )
  cboCombo = ttk.Combobox( panelCombo, values=valCombo, textvariable=varCombo )
  cboCombo.pack( side='left', anchor='w', padx=12, pady=8 )
  
  # make our window 'alwaysontop'
  root.attributes( '-topmost', 1 )
  root.mainloop()
  </code></pre>