You didn't transform (change) the list object referred to by x with this line:
All things considered, that line makes another list object and afterward reassigns the variable x to it. Thus, x currently references the new item, and id(x) gives an unexpected number in comparison to previously:
>>> x=[1,2,4] # x references the list object [1,2,4]
[1, 2, 4]
>>> x=[2,5,3] # x now references an entirely new list object [2,5,3]
[2, 5, 3]
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