[Python] mypy reporting an error in function with generic type

Why does mypy report an error in the code below:

from typing import Self, reveal_type, Protocol


class A:
def dup(self) -> list[Self]:
return [self, self]


class B:
def dup(self) -> list[Self]:
return [self, self]


class C:
def dup(self) -> list[Self]:
return [self, self]


class HasDup(Protocol):
def dup(self) -> list[Self]: ...


def process[T: A | B | C](elem: T) -> list[T]:
reveal_type(elem.dup)
duplicated: list[T] = elem.dup()
return duplicated


process(A())
process(B())
process(C())


The error is:

main.py:25: error: Incompatible types in assignment (expression has type "list[A] | list | list[C]", variable has type "list[T]") [assignment]



If I replace T: A | B | C with T: HasDup or T: (A, B, C), then the error is no longer reported.

Is this a limitation of mypy? It seems to me like A | B | C is a subtype of HasDup.

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