Excess properties not detected when assigning to union type containing a function type #8694

type NormalType = string;
type WorksAsExpected = {a:number, c:number} | NormalType;

let works:WorksAsExpected = {a:1, c:2, d:3} 
/*erro.ts(4,40): error TS2322: Type '{ a: number; c: number; d: number; }' 
is not assignable to type '{ a: number; c: number; } | string'.
  Object literal may only specify known properties, and 'd' does not exist in type 
'{ a: number; c: number; } | string'.*/

type FunctionType = ()=>any;
type DoesntWork = {a:number, c:number} | FunctionType;

let worksTo:DoesntWork = 3 
/*erro.ts(9,5): error TS2322: Type 'number' is not assignable to type 
'{ a: number; c: number; } | (() => any)'.
  Type 'number' is not assignable to type '() => any'.
*/

let doesntWork:DoesntWork = {a:1, c:2, d:3} //no error is displayed