Error output on charts in portfolio

[simpsus]

Traceback (most recent call last):
  File "/home/bastian/workspace/avernus/avernus/gui/charts.py", line 236, in draw_plot
    legend = self.ax.legend(loc="best")
  File "/usr/lib/pymodules/python2.7/matplotlib/axes.py", line 4519, in legend
    self.legend_ = mlegend.Legend(self, handles, labels, **kwargs)
  File "/usr/lib/pymodules/python2.7/matplotlib/legend.py", line 365, in __init__
    self._init_legend_box(handles, labels)
  File "/usr/lib/pymodules/python2.7/matplotlib/legend.py", line 627, in _init_legend_box
    handlebox)
  File "/usr/lib/pymodules/python2.7/matplotlib/legend_handler.py", line 110, in __call__
    handlebox.get_transform())
  File "/usr/lib/pymodules/python2.7/matplotlib/legend_handler.py", line 248, in create_artists
    self.update_prop(p, orig_handle, legend)
  File "/usr/lib/pymodules/python2.7/matplotlib/legend_handler.py", line 71, in update_prop
    self._update_prop(legend_handle, orig_handle)
  File "/usr/lib/pymodules/python2.7/matplotlib/legend_handler.py", line 63, in _update_prop
    self._update_prop_func(legend_handle, orig_handle)
  File "/usr/lib/pymodules/python2.7/matplotlib/legend_handler.py", line 36, in update_from_first_child
    tgt.update_from(src.get_children()[0])
IndexError: list index out of range