Element disappear after adding custom animations

I have a slide with multiple lines:

  • a
  • b
  • c
  • d

I’d like an animation that a and c are always visible, but b and d appear after a mouse click.

When I apply a custom animation to b, everything works: all but b are visible, and b appears after a click.

But when I apply the same animation to d, c is no longer visible, neither before nor after the click.

I’ve recorded a screencast showing the problem.

I’m using on Ubuntu (Build ID: 1:5.1.4-0ubuntu1)