Bug report

Bug summary

line.set_ydata should update a drawn line, however this seems to break under some circumstances, depending on the background color.

Code for reproduction

fig,ax = plt.subplots(facecolor='none')
ax.set_facecolor('none')

plt.subplots_adjust(left=0.25, bottom=0.25)
plt.axis([0, 4, 0,2])
l, = ax.plot([1,2,3],[1,0,1])
ax.set_title('down')
def update():
    l.set_ydata([1,2,1])
    ax.set_title('up')

this creates a 'v' shape with title 'down' as expected, but then calling update()

leads to this:

It continuously draws over the previous plot. fig.canvas.draw() doesn't help, but if I fig.savefig('test.jpg') it updates correctly.

If the axis background is set to something else but 'none' , the lines updates correctly, but the title doesn't. The title only update correctly, if also the figure background is something else but 'none'.

Expected outcome

• The update function should immediately update the interactive figure.

Matplotlib version

• Matplotlib version: 2.0.0
• Python version: 3.6.0 (but same issue with 2.7.13)
• Platform: OSX
• How did you install Matplotlib and Python: anaconda