Possible bug in Group

I have random NullPointerException at com.badlogic.gdx.scenes.scene2d.Group.drawChildren (SourceFile:79).

What happens if an actor is added between line 68 and line 77 ?

I think children.size is incremented, but the actor is obviously not added in actors SnapshotArray, so the last child is null.

What do you think ?

Thanks for your time :)