1)Run the attached test. In the controls UI, change the start Angle, Length of the arc to values close to max and min.
Also play around with the various other controls except for Scale & Shear sliders (as they expose another bug already filed RT-871).
1)Now change the rotation angle of the Arc by increasing and decreasing the rotation slider value in small increments. Painting artifacts can be seen.
Test and snapshot are attached for reference.