Traceback on Close() of a wx.Dialog

[Werner F. Bruhin]

I client of mine is reporting an exception which I can not duplicate nor 
can I think of what is causing it.

Maybe someone here can shed some light on this.

The exception is:
Traceback (most recent call last):
  File "dialogerror.pyo", line 475, in OnClearButton
  File "wx\_core.pyo", line 8093, in Close
PyAssertionError: C++ assertion "!(lvi.mask & LVIF_STATE)" failed in 
..\..\src\msw\listctrl.cpp(2284): we don't support state callbacks yet!

The code in OnClearButton is:
    def OnClearButton(self, event):
        self.ClearAllFiles()
        self.Close()

"self" is a wx.Dialog

Thanks for any hints
Werner