[Bug Report] carousel unexpected change event emitted

[Meowu]

Element UI version

2.4.11

OS/Browsers version

All

Vue version

2.5.21

Reproduction Link

https://codepen.io/vamdoose/pen/rEMPLr?editors=1111

Steps to reproduce

1. listen an change event on the carousel component.
2. when the component created, the active index is set to 0 and emits an change event.

What is Expected?

the data prop activeIndex set 0 as the initial value instead of -1 .

What is actually happening?

Since the component created, the active index changes from -1 to 0 and emits the change event.

Is that an intended phenomenon or unexpected issue ?
Why not just set the initial data prop activeIndex to 0 instead of -1.