golang 求助大佬

import "fmt"

func main() {
    input := []int{2,3, 5}
    target := 8
    fmt.Println(combinationSum(input, target))

}

func combinationSum(candidates []int, target int) [][]int {
   var res [][]int

   var backtrack func(int, int, []int)
   backtrack = func(idx int, sum int, nums []int) {

       if sum == target {
           res = append(res, nums)
       }
       if sum >= target {
           return
       }
       for i := idx; i < len(candidates); i++ {
           backtrack(i, sum + candidates[i], append(nums,candidates[i]))
       }
   }
   backtrack(0, 0, []int{})
   return res
}

这段代码结果有问题， 而且问题处在 res = append(res, nums) 这一行， 如果我把 nums copy 一个再 append 就不会有问题了，听说这里大神比较多，求大神们指教一下