problem: clipboard (erroneously) converts contents to unicode

Hi-
  I'm trying to get at the contents of the
clipboard in order to convert the data there
with the unicode() function. The problem is,
by the time I get the data, it has already
been converted to unicode (assuming the wrong
source encoding), and I cannot convert it (1).

# Get GB-encoded text from clipboard &
# put in data object
do = wx.TextDataObject()
wx.TheClipboard.Open()
success = wx.TheClipboard.GetData(do)
wx.TheClipboard.Close()
# Convert data to unicode
gbText = do.GetText()
print "type(gbText) =", type(gbText)
uniText = unicode( gbText, "gb18030")

output:

type(gbText) = <type 'unicode'>
TypeError: decoding Unicode is not supported

Win 2000, python 2.3.2, wx 2.4.2.4u

I don't know it this is related to Windows
or to wx.TextDataObject, which is derived
from wx.DataObject, a 'smart' piece of data
(perhaps too 'smart' here). Is there a way
I can get the data from the clipboard in its
original form, before it is (inaccurately)
converted to unicode?

Thanks, John

(1) I am copying simplified Chinese text in
the GB standard, the format in which it is
usually found, and need to paste it into an
STC in a unicode-aware wxPython app; to
display correctly, the text has to be converted
to unicode.)