Vue wrong twice time adding object on cloned object using splice()

vue push wrong twice time on newly added object,
code is https://codesandbox.io/s/vue-template-qnj20
my code on sandbox

i have two component one is main component and another one is for clone.my problem is excess reactivity,i have a list from parent and passing to child by props and on my child component, i have a two button, first button for cloning object and add it to the same list from parent,and second button for update object into the 1st list while add the object is added it to the cloned object too.i tried code attached below

I’m not sure, what you want to achieve. But what you do in your code (changing parent’s data in a child component) looks wrong. The way to go when passing data back and forth would be parent to child by props and child to parent by events.