Combine.Publisher.flatMap issue

CombineFlatMapIssue.swift

import Combine

enum MyError: Error {
    case error
}

let subject1 = PassthroughSubject<Int, Error>()

let cancellable1 = subject1
    .print("before flatMap")
    .flatMap { _ in
        Fail<Int, Error>(error: MyError.error)
    }
    .print("after flatMap")
    .sink {
        print("completion: \($0)")
    } receiveValue: {
        print("receiveValue: \($0)")
    }

print("Sending 1")
subject1.send(1)
print("Sending 2")
subject1.send(2)
print("Cancelling")
cancellable1.cancel()
print("Sending 3")
subject1.send(3)

extension Publisher {
    func flatMap2<T, P>(
        maxPublishers: Subscribers.Demand = .unlimited,
        _ transform: @escaping (Self.Output) -> P
    ) -> AnyPublisher<T, Failure>
    where T == P.Output, P : Publisher, Self.Failure == P.Failure {
        flatMap(maxPublishers: maxPublishers) {
            transform($0)
                .map { value -> Result<T, Failure> in
                    Result.success(value)
                }
                .catch {
                    return Just<Result<T, Failure>>(Result.failure($0))
                }
        }
        .tryMap { result in
            switch result {
            case let .success(value):
                return value
            case let .failure(error):
                throw error
            }
        }
        .mapError { error in
            error as! Failure
        }
        .eraseToAnyPublisher()
    }
}

print("-----------------")

let subject2 = PassthroughSubject<Int, Error>()

let cancellable2 = subject2
    .print("before flatMap")
    .flatMap2 { _ in
        Fail<Int, Error>(error: MyError.error)
    }
    .print("after flatMap")
    .sink {
        print("completion: \($0)")
    } receiveValue: {
        print("receiveValue: \($0)")
    }

print("Sending 1")
subject2.send(1)
print("Sending 2")
subject2.send(2)
print("Cancelling")
cancellable2.cancel()
print("Sending 3")
subject2.send(3)

/*

output:

after flatMap: receive subscription: (FlatMap)
after flatMap: request unlimited
before flatMap: receive subscription: (PassthroughSubject)
before flatMap: request unlimited
Sending 1
before flatMap: receive value: (1)
after flatMap: receive error: (error)
completion: failure(__lldb_expr_13.MyError.error)
Sending 2
before flatMap: receive value: (2)
Cancelling
Sending 3
before flatMap: receive value: (3)
-----------------
after flatMap: receive subscription: (TryMap)
after flatMap: request unlimited
before flatMap: receive subscription: (PassthroughSubject)
before flatMap: request unlimited
Sending 1
before flatMap: receive value: (1)
before flatMap: receive cancel
after flatMap: receive error: (error)
completion: failure(__lldb_expr_13.MyError.error)
Sending 2
Cancelling
Sending 3

*/