Hello
Their  is  no connection between lp:956798and this bug. 
Here Stock Graph report is generate using PyChart which is Independent  to Server Report Engine.
Being more specific the trackback looks like this :
2012-08-29 06:05:34,223 5050 ERROR ? openerp.service.web_services: Exception: 'charmap' codec can't encode characters in position 0-7: character maps to <undefined>
Traceback (most recent call last):
  File "/home/openerp/source/server/trunk/openerp/service/web_services.py", line 726, in go
    (result, format) = obj.create(cr, uid, ids, datas, context)
  File "/home/openerp/source/addons/trunk/stock/report/product_stock.py", line 108, in create
    gt.draw()
  File "/home/openerp/source/addons/trunk/stock/report/stock_graph.py", line 101, in draw
    ar.draw(self._canvas)
  File "/usr/lib/pymodules/python2.7/pychart/area.py", line 248, in draw
    self.legend.draw(self, legends, can)
  File "/usr/lib/pymodules/python2.7/pychart/legend.py", line 178, in draw
    l.draw(ar, can, this_x, this_x + max_sample_width[col], this_y)
  File "/usr/lib/pymodules/python2.7/pychart/legend.py", line 88, in draw
    can.show(x_label, y, self.label)
  File "/usr/lib/pymodules/python2.7/pychart/basecanvas.py", line 503, in show
    self.text_show(font_name, nscale(size), color, str)
  File "/usr/lib/pymodules/python2.7/pychart/pdfcanvas.py", line 171, in text_show
    self.__write("(%s) Tj " % (str.encode('mac_roman')))
  File "/usr/lib/python2.7/encodings/mac_roman.py", line 12, in encode
    return codecs.charmap_encode(input,errors,encoding_table)
UnicodeEncodeError: 'charmap' codec can't encode characters in position 0-7: character maps to <undefined>
2012-08-29 06:05:34,436 5050 ERROR None openerp.netsvc: charmap
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0
8
character maps to <undefined>
(<type 'exceptions.UnicodeEncodeError'>, UnicodeEncodeError('charmap', u'\u0410\u043d\u0430\u0442\u043e\u043b\u0438\u0439 \u0623\u0646\u0627\u062a\u0648\u0644\u064a \u963f\u7eb3\u6258\u5229 \u30a2\u30ca\u30c8\u30fc\u30ea\u30fc \uc544\ub098\ud1a8\ub9ac \u0905\u0928\u093e\u0924\u094b\u0932\u0940 \u0e2d\u0e32\u0e19\u0e32\u0e42\u0e15\u0e25\u0e35 \u0622\u0646\u0627\u062a\u0648\u0644\u06cc', 0, 8, 'character maps to <undefined>'), <traceback object at 0xb4d9e64>)
Traceback (most recent call last):
  File "/home/openerp/source/server/trunk/openerp/netsvc.py", line 362, in dispatch_rpc
    result = ExportService.getService(service_name).dispatch(method, params)
  File "/home/openerp/source/server/trunk/openerp/service/web_services.py", line 669, in dispatch
    res = fn(db, uid, *params)
  File "/home/openerp/source/server/trunk/openerp/service/web_services.py", line 774, in exp_report_get
    return self._check_report(report_id)
  File "/home/openerp/source/server/trunk/openerp/service/web_services.py", line 752, in _check_report
    netsvc.abort_response(exc, exc.message, 'warning', exc.traceback)
  File "/home/openerp/source/server/trunk/openerp/netsvc.py", line 67, in abort_response
    raise openerp.osv.osv.except_osv(description, details)
except_osv: (u'charmap\n\u0410\u043d\u0430\u0442\u043e\u043b\u0438\u0439 \u0623\u0646\u0627\u062a\u0648\u0644\u064a \u963f\u7eb3\u6258\u5229 \u30a2\u30ca\u30c8\u30fc\u30ea\u30fc \uc544\ub098\ud1a8\ub9ac \u0905\u0928\u093e\u0924\u094b\u0932\u0940 \u0e2d\u0e32\u0e19\u0e32\u0e42\u0e15\u0e25\u0e35 \u0622\u0646\u0627\u062a\u0648\u0644\u06cc\n0\n8\ncharacter maps to <undefined>', (<type 'exceptions.UnicodeEncodeError'>, UnicodeEncodeError('charmap', u'\u0410\u043d\u0430\u0442\u043e\u043b\u0438\u0439 \u0623\u0646\u0627\u062a\u0648\u0644\u064a \u963f\u7eb3\u6258\u5229 \u30a2\u30ca\u30c8\u30fc\u30ea\u30fc \uc544\ub098\ud1a8\ub9ac \u0905\u0928\u093e\u0924\u094b\u0932\u0940 \u0e2d\u0e32\u0e19\u0e32\u0e42\u0e15\u0e25\u0e35 \u0622\u0646\u0627\u062a\u0648\u0644\u06cc', 0, 8, 'character maps to <undefined>'), <traceback object at 0xb4d9e64>))

I suggest community Team to have a look at and take appropriate Decision (Does not affect server project).
Thanks in advance for understanding.