Removing an element from a slice duplicates the last element in Go?

Question

I was playing with slices in go to better understand the behaviour. I wrote the following code:

func main() {
    // Initialize
    myslice := []int{1, 2, 3, 4, 5, 6, 7, 8, 9}
    newSlice := myslice

    fmt.Println(myslice)
    fmt.Println(newSlice)

    removeIndex := 3
    newSlice = append(newSlice[:removeIndex], newSlice[removeIndex+1:]...)
    fmt.Println(myslice)
    fmt.Println(newSlice)


}

This is the output:

[1 2 3 4 5 6 7 8 9]
[1 2 3 4 5 6 7 8 9]

[1 2 3 5 6 7 8 9 9]
[1 2 3 5 6 7 8 9]

I dont really understand what happens with newSlice that duplicates the 9 at the end. Also, does this mean, that this operation removes the given element from the underlying array?

https://go.dev/play/p/pf7jKw9YcfL