This happens because of how Python handles list multiplication. Here's a full example:

---

### Example:

```python

# Works as expected

matrixM = [[0,0,0,0],[0,0,0,0],[0,0,0,0],[0,0,0,0]]

matrixM[1][1] = 2

print(matrixM)

# Output: [[0, 0, 0, 0], [0, 2, 0,]()]()

Correct Way:

Use a list comprehension to create independent sublists:

matrixA = [[0]*4 for _ in range(4)]

matrixA[1][1] = 2

print(matrixA)

# Output: [[0, 0, 0, 0], [0, 2, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]