Windows gtk client crashes on charts drawing

Hello.
I've posted this once, but it was refused due the bug hasn't been reproduced.
I'll try once again, describing the conditions of appearing the bug as detailed as possible.
Let's take a default database with demo data. In one of the production orders we shall set Repair Workhop as a workcenter(by default we have all oders appointed to Assembly Workshop). Now let's select Reporting->Workcenter loads. Normally we should see 2 workcenters and 4 time periods. Web client displays it fine, but windows gtk client crushes:ile "widget\view\graph_gtk\graph.pyo", line 113, in display

File "tinygraph\__init__.pyo", line 123, in tinygraph
File "matplotlib\axes.pyo", line 3617, in legend
File "matplotlib\legend.pyo", line 182, in __init__
File "matplotlib\legend.pyo", line 248, in _get_handles
File "matplotlib\cbook.pyo", line 900, in safezip
ValueError: In safezip, len(args[0])=4 but len(args[1])=2

It happens in the following code:
if len(axis_group)>1:
                axis_group = map(lambda x: x.split('/')[-1], axis_group)
                subplot.legend(gvalue2,axis_group,shadow=True,loc='best',prop = font_property)
            else:
                  t1 = [ axis_data[x]['string'] for x in axis[1:]]
                  subplot.legend(gvalue,t1,shadow=True,loc='best',prop = font_property)

The first two arguments of legend function must be of equal length, but in fact the debugger shows:
ais_group=list: ['Assembly workshop', 'Repairs workshop'] (2 items)
gvalue2=list: [<matplotlib.patches.Rectangle object at 0x0315F110>, <matplotlib.patches.Rectangle object at 0x0315FC10>, <matplotlib.patches.Rectangle object at 0x0316A6F0>, <matplotlib.patches.Rectangle obje...

(4 items)

There are 4 bars and 2 items in legend.
I removed the code that checks lenght of the arguments in safezip function of matlotlib as a temp solution and nothing bad happened, it displayed the chart.
I'm not sure how to fix it: maybe it must be gvalue instead gvalue2 in the third string?