I had the same problem 2 monthes ago. It comes from this line in your example
code :
cb1=wx.ComboBox(self, wx.NewId(), "", choices=["", "Home", "Business"],
style=wx.CB_READONLY)
To correct, just modify the first value from the choices list :
choices=[" ", "Home", "Business"]
because, it doesn't support to have a empty string
I don't know if it is further a bug, but it works this way.
Sebastien Treyvaud
Switzerland