Store: Handling of @ngrx/store/update-reducers Action on Startup leads to strange behaviour for initialStates

[tnobody]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[x] Bug report  
[ ] Feature request
[ ] Documentation issue or request

What is the current behavior?

I configure a object as an initialState for the store. Unfortunately some values are "overridden" on start-up of the store/app.

Expected behavior:

All properties from the initial-state should remain untouched by any internal ngrx-action.

Minimal reproduction of the problem with instructions:

I think my explanation was i bit poor sofar (sorry it's hard to explain this). I think an example will show the problem:

https://stackblitz.com/edit/angular-6wbjq4

In this example everything is fine. The initial state is produced by the initState() function in app/app.state.ts.

BUT:

Remove the key 'featureB' from this init state will "break" this behaviour.

It seems to be caused by the combination function:

platform/modules/store/src/utils.ts

Lines 29 to 44 in 9b02f79

	return function combination(state, action) {
	state = state === undefined ? initialState : state;
	let hasChanged = false;
	const nextState: any = {};
	for (let i = 0; i < finalReducerKeys.length; i++) {
	const key = finalReducerKeys[i];
	const reducer: any = finalReducers[key];
	const previousStateForKey = state[key];
	const nextStateForKey = reducer(previousStateForKey, action);
	nextState[key] = nextStateForKey;
	hasChanged = hasChanged || nextStateForKey !== previousStateForKey;
	}
	return hasChanged ? nextState : state;
	};
	}

The function expects all possible state properties to be setted. If a property is not (in initialState) set the 'hasChanged' turns true and returns the nextState. This is some kind of an intermediated state (at least while the ' @ngrx/store/update-reducers'-Action is fired).

Version of affected browser(s),operating system(s), npm, node and ngrx:

@ngrx/store v 5.1 + 5.2

Other information:

This is not directly linked to the problem but another finding that confused me.
After '@ngrx/store/update-reducers' is fired all reducers are applied, even if they were already applied previously:

[russelporosky]

+1 We're seeing the repetition issue here as well on feature stores. The first feature will repeat 3 times, the second one repeats 4 times. Weird. In our case it's not causing any problems.

[johannesjo]

I'm experiencing the same thing with v6.1.0.