Why do I need to use copy in recursion (climbing stairs problems)

Question

I was solving one of the problems from classic interview sets and I met a strange issue. The task is to by given number of stairs n and possible moves (steps) range(1,k) return all the possible combinations for steps. My solution works just if I use copy.copy successful steps combination before appending it to the all-solutions-array. Does anyone know the reason why ??

import copy
def climbingStaircase(n, k, successful_steps, steps_made):
    print(n, k, successful_steps, steps_made)

    # if there n is less than 0 --> return
    if n < 0:
        print('entering here')

        return
    # if n  == 0 -> we reached the top of the stairs
    if n == 0:

        successful_steps.append(copy.copy(steps_made))

        print('entering 0')
        print(n, k, successful_steps, steps_made)
        return

    for step in range(1,k+1):


        n -= step
        steps_made.append(step)


        climbingStaircase(n, k, successful_steps, steps_made) # 0, 2, [[1,1,1,1]] [1,1,1,1]
        n += steps_made.pop() #
        # steps_made.pop()

    return

def countWays(n, k):
    successful_steps = []
    climbingStaircase(n, k,successful_steps, [])
    print(successful_steps)

countWays(4,2)

For example for 4,2 with copy, I get the solution:

[[1, 1, 1, 1], [1, 1, 2], [1, 2, 1], [2, 1, 1], [2, 2]]

If I do not use copy function, everything seems wrong, it seems as if by editing, adding and popping from steps_made I am still somehow influencing the successful steps