RuntimeError: libpng signaled error

Sometimes I am getting this error with the trunk version. Not sure what a MWE would be. Has anyone encountered this?
Thanks, Chaffra

RuntimeError                              Traceback (most recent call last)
/usr/local/lib/python3.6/dist-packages/ipympl/backend_nbagg.py in _handle_message(self, object, content, buffers)
    178             self.manager.resize(w, h)
    179         else:
--> 180             self.manager.handle_json(content)
    181 
    182     def send_json(self, content):

/usr/local/lib/python3.6/dist-packages/matplotlib/backends/backend_webagg_core.py in handle_json(self, content)
    437 
    438     def handle_json(self, content):
--> 439         self.canvas.handle_event(content)
    440 
    441     def refresh_all(self):

/usr/local/lib/python3.6/dist-packages/matplotlib/backends/backend_webagg_core.py in handle_event(self, event)
    238         handler = getattr(self, 'handle_{0}'.format(e_type),
    239                           self.handle_unknown_event)
--> 240         return handler(event)
    241 
    242     def handle_unknown_event(self, event):

/usr/local/lib/python3.6/dist-packages/matplotlib/backends/backend_webagg_core.py in handle_draw(self, event)
    254 
    255     def handle_draw(self, event):
--> 256         self.draw()
    257 
    258     def _handle_mouse(self, event):

/usr/local/lib/python3.6/dist-packages/matplotlib/backends/backend_webagg_core.py in draw(self)
    151             super().draw()
    152         finally:
--> 153             self.manager.refresh_all()  # Swap the frames.
    154 
    155     def draw_idle(self):

/usr/local/lib/python3.6/dist-packages/matplotlib/backends/backend_webagg_core.py in refresh_all(self)
    441     def refresh_all(self):
    442         if self.web_sockets:
--> 443             diff = self.canvas.get_diff_image()
    444             if diff is not None:
    445                 for s in self.web_sockets:

/usr/local/lib/python3.6/dist-packages/matplotlib/backends/backend_webagg_core.py in get_diff_image(self)
    199             buff = _png.write_png(
    200                 output.view(dtype=np.uint8).reshape(output.shape + (4,)),
--> 201                 None, compression=6, filter=_png.PNG_FILTER_NONE)
    202 
    203             # Swap the renderer frames

RuntimeError: libpng signaled error

从 ipympl 的 backend_nbagg.py 以及 matplotlib 在 backend_webagg_core.py 中经过 handle_draw()、refresh_all() 和 get_diff_image() 的路径入手，尤其关注 traceback 中显示的 _png.write_png 调用。使用报告中的 Python、ipympl、matplotlib 和 libpng 版本复现该故障，然后定义一个最小示例和回归测试覆盖范围，以证明该错误不再发生。