Confirmed on Windows XP, Inkscape 0.46, 0.47 and bzr rev. 9275. Blank python command box.
Also confirmed on Ubuntu 9.10, Inkscape 0.47 and bzr rev. 9288, Uniconvertor 1.1.4, but I also get an error message (and of course no command box...).
Exporting simple shapes (rectangles and ellipses) works well on both operating systems with all Inkscape versions.

Error message:
---
UniConvertor failed:

Cannot list directory /home/nicolas/.uniconvertor:[Errno 2] No such file or directory: '/home/nicolas/.uniconvertor'
ignoring it in font_path
Cannot list directory /home/nicolas/.uniconvertor:[Errno 2] No such file or directory: '/home/nicolas/.uniconvertor'
ignoring it in font_path
/usr/lib/pymodules/python2.6/uniconvertor/app/utils/locale_utils.py:9: DeprecationWarning: The popen2 module is deprecated.  Use the subprocess module.
  from popen2 import popen2
No plugin-type information in /usr/lib/pymodules/python2.6/uniconvertor/app/plugins/Filters/__init__.py
I can't find font Arial. I'll use Slim instead
Fontsystem not yet implemented in UniConvertor. See /usr/share/doc/python-uniconvertor/README.Debian for more info
I can't find font Balloon XBd BT. I'll use Slim instead
Fontsystem not yet implemented in UniConvertor. See /usr/share/doc/python-uniconvertor/README.Debian for more info
No plugin-type information in /usr/lib/pymodules/python2.6/uniconvertor/app/plugins/Filters/__init__.py
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/pymodules/python2.6/uniconvertor/__init__.py", line 88, in uniconv
    saver(doc, output_file)
  File "/usr/lib/pymodules/python2.6/uniconvertor/app/plugins/plugins.py", line 201, in __call__
    module.save(document, file, filename, options)
  File "/usr/lib/pymodules/python2.6/uniconvertor/app/plugins/Filters/wmfsaver.py", line 461, in save
    saver.SaveDocument(document)
  File "/usr/lib/pymodules/python2.6/uniconvertor/app/plugins/Filters/wmfsaver.py", line 403, in SaveDocument
    left, bottom, right, top = doc.BoundingRect()
  File "/usr/lib/pymodules/python2.6/uniconvertor/app/Graphics/document.py", line 221, in BoundingRect
    rect = layer.bounding_rect
  File "/usr/lib/pymodules/python2.6/uniconvertor/app/Graphics/base.py", line 352, in __getattr__
    getattr(self, method)()
  File "/usr/lib/pymodules/python2.6/uniconvertor/app/Graphics/compound.py", line 174, in update_rects
    boxes = map(lambda o: o.coord_rect, self.objects)
  File "/usr/lib/pymodules/python2.6/uniconvertor/app/Graphics/compound.py", line 174, in <lambda>
    boxes = map(lambda o: o.coord_rect, self.objects)
  File "/usr/lib/pymodules/python2.6/uniconvertor/app/Graphics/base.py", line 352, in __getattr__
    getattr(self, method)()
  File "/usr/lib/pymodules/python2.6/uniconvertor/app/Graphics/compound.py", line 174, in update_rects
    boxes = map(lambda o: o.coord_rect, self.objects)
  File "/usr/lib/pymodules/python2.6/uniconvertor/app/Graphics/compound.py", line 174, in <lambda>
    boxes = map(lambda o: o.coord_rect, self.objects)
  File "/usr/lib/pymodules/python2.6/uniconvertor/app/Graphics/base.py", line 352, in __getattr__
    getattr(self, method)()
  File "/usr/lib/pymodules/python2.6/uniconvertor/app/Graphics/text.py", line 492, in update_rects
    rect = apply(Rect, a.font.TextBoundingBox(self.text, a.font_size, a))
TypeError: TextBoundingBox() takes exactly 3 arguments (4 given)