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First, a note: your page says to report bugs in launchpad, but launchpad says they are not your bug tracker.

Now the bug:

In load_drawing, you do this:

if type(filename) == StringType: [handle it as a filename]
else: [handle it as a file object]

The problem is that unicode strings fall in the "handle as a file object" side.

You may want to do

if type(filename) in StringTypes

instead