AnimationGroup with negative z_index

[nubDotDev]

Description of bug / unexpected behavior

When an AnimationGroup acts on a Mobject with a negative z_index, the animation doesn't actually play.

Expected behavior

Ideally, using an AnimationGroup should work. It did with a previous stable version so this must be a recent bug.

How to reproduce the issue

Code for reproducing the problem

class Test(Scene):
    def construct(self):
        s = Square().set_z_index(-1)
        self.play(GrowFromCenter(s)) # Works great
        self.wait()
        self.play(AnimationGroup(GrowFromCenter(s))) # Doesn't work
        self.wait()

Additional media files

Images/GIFs

[vaclavblazej]

I can confirm that this is indeed the current behavior.
First version that exhibits it is 0.15.1:

0.15.1 behavior video

0.15.1.mp4

The same code behaves in 0.15.0 as follows:

0.15.0 behavior video

0.15.0.mp4