Unexpected behavior when emitting actions synchronously

[robmcm]

Unexpected behavior when emitting actions synchronously

What is the current behavior?
When an epic dispatches an action synchronously, it will in turn synchronously call store.dispatch (https://github.com/redux-observable/redux-observable/blob/master/src/createEpicMiddleware.ts#L85). This means all reducers and epics will be called with the new action before the current action propagates through the remaining combined epics. This causes some confusion where the state$.value can differ from what would be expected (even inside the same state$ pipe).

If the current behavior is a bug, please provide the steps to reproduce and a minimal demo of the problem using JSBin, StackBlitz, or similar.

(action$, state$, dependencies) => {
    const initialState = state$.value; // Initial state
    return state$.pipe(
        tap(state => console.log(state === initialState), // Will return false
        startWith(actionToChangeState) // This action will be run through the reducers before state$ is subscribed to above
   )
}

What is the expected behavior?
I would expect the epics to dispatch actions after the current action/state has been passed to each epic in combine epics.
However I understand this has probably been around for a while, and may only crop up in more complex use cases (with multiple epics).
A workaround is to add delay(1) to the end of any epic that dispatches synchronously (specifically in response to an emit on state$ or action$).
If this is unlikely to be fixed it may be good to have it added to a "known issues" section in the docs?

Which versions of redux-observable, and which browser and OS are affected by this issue? Did this work in previous versions of redux-observable?
I think it has always been like this.

[robmcm]

If epic1 dispatches action2 synchronously

Expected order:
reducer1(action1, state1),
reducer2(action1, state1),
epic1(action1, state1), // Dispatches action2, but waits for all epics to be called with current state/action
epic2(action1, state1),

reducer1(action2, state2),
reducer2(action2, state2),
epic1(action2, state2),
epic2(action2, state2)

Actual :
reducer1(action1, state1),
reducer2(action1, state1),
epic1(action1, state1), // Dispatches action2 and dispatch starts a new cycle
reducer1(action2, state2),
reducer2(action2, state2),
epic1(action2, state2),
epic2(action2, state2),
epic2(action1, state1),