Publishers.MakeConnectable leaks upstream publisher?

Using Swift
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1

I'm having trouble with Swift Combine resulting in leaks of upstream publishers, specifically when using makeConnectable(). I have created demo code to highlight the issue but it's complicated, so let me break down the variables:

  1. Synchronously vs Asynchronously cancelling the connection returned by MakeConnectable.connect().
  2. Storing Publisher.MakeConnectable in a local variable.
  3. Finishing or leaving the upstream publisher in an unfinished state.

3 variables results in 8 expanded cases. Here are the results:

Cancel Timing Local Variable Finish Upstream Bad Result (Leak)
SYNC YES YES NO
ASYNC YES YES NO
SYNC YES NO NO
ASYNC YES NO YES
SYNC NO YES NO
ASYNC NO YES NO
SYNC NO NO YES
ASYNC NO NO YES
See Code 
let pubCancelSyncThenFinishIndirect = PassthroughSubject<Void, Never>()
let pubCancelAsyncThenFinishIndirect = PassthroughSubject<Void, Never>()
let pubCancelSyncNoFinishIndirect = PassthroughSubject<Void, Never>()
let pubCancelAsyncNoFinishIndirect = PassthroughSubject<Void, Never>() // <- leaks
let pubCancelSyncThenFinishDirect = PassthroughSubject<Void, Never>()
let pubCancelAsyncThenFinishDirect = PassthroughSubject<Void, Never>()
let pubCancelSyncNoFinishDirect = PassthroughSubject<Void, Never>()    // <- leaks
let pubCancelAsyncNoFinishDirect = PassthroughSubject<Void, Never>()   // <- leaks
let cancelSyncThenFinishConnectable = pubCancelSyncThenFinishIndirect.makeConnectable()
let cancelAsyncThenFinishConnectable = pubCancelAsyncThenFinishIndirect.makeConnectable()
let cancelSyncNoFinishConnectable = pubCancelSyncNoFinishIndirect.makeConnectable()
let cancelAsyncNoFinishConnectable = pubCancelAsyncNoFinishIndirect.makeConnectable()
let cancelSyncThenFinishConnectionIndirect = cancelSyncThenFinishConnectable.connect()
let cancelAsyncThenFinishConnectionIndirect = cancelAsyncThenFinishConnectable.connect()
let cancelSyncNoFinishConnectionIndirect = cancelSyncNoFinishConnectable.connect()
let cancelAsyncNoFinishConnectionIndirect = cancelAsyncNoFinishConnectable.connect()
let cancelSyncThenFinishConnectionDirect = pubCancelSyncThenFinishDirect.makeConnectable().connect()
let cancelAsyncThenFinishConnectionDirect = pubCancelAsyncThenFinishDirect.makeConnectable().connect()
let cancelSyncNoFinishConnectionDirect = pubCancelSyncNoFinishDirect.makeConnectable().connect()
let cancelAsyncNoFinishConnectionDirect = pubCancelAsyncNoFinishDirect.makeConnectable().connect()
cancelSyncThenFinishConnectionIndirect.cancel()
cancelSyncNoFinishConnectionIndirect.cancel()
cancelSyncThenFinishConnectionDirect.cancel()
cancelSyncNoFinishConnectionDirect.cancel()
DispatchQueue.main.async {
	cancelAsyncThenFinishConnectionIndirect.cancel()
	cancelAsyncNoFinishConnectionIndirect.cancel()
	cancelAsyncThenFinishConnectionDirect.cancel()
	cancelAsyncNoFinishConnectionDirect.cancel()
	pubCancelSyncThenFinishIndirect.send(completion: .finished)
	pubCancelAsyncThenFinishIndirect.send(completion: .finished)
	pubCancelSyncThenFinishDirect.send(completion: .finished)
	pubCancelAsyncThenFinishDirect.send(completion: .finished)
}
DispatchQueue.main.asyncAfter(deadline: .now() + 4) { [
	weak pubCancelSyncThenFinishIndirect,
	weak pubCancelAsyncThenFinishIndirect,
	weak pubCancelSyncNoFinishIndirect,
	weak pubCancelAsyncNoFinishIndirect,
	weak pubCancelSyncThenFinishDirect,
	weak pubCancelAsyncThenFinishDirect,
	weak pubCancelSyncNoFinishDirect,
	weak pubCancelAsyncNoFinishDirect,
] in
	print("*** pubCancelSyncThenFinishIndirect is still alive: \(pubCancelSyncThenFinishIndirect == nil ? "NO" : "YES")")
	print("*** pubCancelAsyncThenFinishIndirect is still alive: \(pubCancelAsyncThenFinishIndirect == nil ? "NO" : "YES")")
	print("*** pubCancelSyncNoFinishIndirect is still alive: \(pubCancelSyncNoFinishIndirect == nil ? "NO" : "YES")")
	print("*** pubCancelAsyncNoFinishIndirect is still alive: \(pubCancelAsyncNoFinishIndirect == nil ? "NO" : "YES")")
	print("*** pubCancelSyncThenFinishDirect is still alive: \(pubCancelSyncThenFinishDirect == nil ? "NO" : "YES")")
	print("*** pubCancelAsyncThenFinishDirect is still alive: \(pubCancelAsyncThenFinishDirect == nil ? "NO" : "YES")")
	print("*** pubCancelSyncNoFinishDirect is still alive: \(pubCancelSyncNoFinishDirect == nil ? "NO" : "YES")")
	print("*** pubCancelAsyncNoFinishDirect is still alive: \(pubCancelAsyncNoFinishDirect == nil ? "NO" : "YES")")
}

I would really appreciate it if someone can explain why this code consistently keeps the upstream publisher alive in some cases when I would expect it to disappear in every case.