Router CanDeactivate runs twice when back button is pressed

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Current behavior CanDeactivate guard runs twice if i use browser back button and canDeactivate returns promise or observable (any delayed result). If i return true/false it will execute once. If i use links to navigate it also work fine. The problem is that i can’t create plunker 😦 Relevant logs:

RouterEvent(type='routeStart', id='3', url=/dashboard/master/department/list)
RouterEvent(type='routeRecognize', id='3', url=undefined, urlAfterRedirects=/dashboard/master/department/list, state=Route(url:'', path:'') { Route(url:'dashboard', path:'dashboard') { Route(url:'master/department/list', path:'master/department/list') }  } )
canDeactivatePageDetailsComponent1.canDeactivate
RouterEvent(type='routeStart', id='4', url=/dashboard/master/department/list)
RouterEvent(type='routeRecognize', id='4', url=undefined, urlAfterRedirects=/dashboard/master/department/list, state=Route(url:'', path:'') { Route(url:'dashboard', path:'dashboard') { Route(url:'master/department/list', path:'master/department/list') }  } )
canDeactivatePageDetailsComponent1.canDeactivate
RouterEvent(type='routeCancel', id='3', url=/dashboard/master/department/list)
RouterEvent(type='routeEnd', id='4', url=/dashboard/master/department/list, urlAfterRedirects=/dashboard/master/department/list)
RouterEvent(type='routeSuccess', id='4', url=/dashboard/master/department/list, urlAfterRedirects=/dashboard/master/department/list)

It looks like navigation was fired twice.

Expected behavior Should be executed once and wait for result.

Reproduction of the problem

public canDeactivate(component:any, route:ActivatedRouteSnapshot, state:RouterStateSnapshot):Observable<boolean>|Promise<boolean>|boolean
    {
        console.trace('canDeactivate?');
        return new Promise<boolean>((resolve)=>{
            setTimeout(()=>{
                resolve(true);
            }, 1000);
        });
    }

What is the motivation / use case for changing the behavior? It results in two confirm dialogs. I would really appreciate solution to this.

• Angular version: 2.0.0-final
• Browser: [all]
• Language: [TypeScript 1.8]