TS losing optional properties when used with index signature and generics

[asvetliakov]

TypeScript Version: 2.0.0-beta

Code

Base code:

// A *self-contained* demonstration of the problem follows...
 interface Test {
 a?: number;
 b?: string;
 }
 interface TestWithStrictProp {
 a?: number;
 b?: string;
 c: string;
 }

 interface TestIndex {
 [key: string]: Test;
 }
 interface TestIndexWithStrict {
 [key: string]: TestWithStrictProp;
 }
 declare function testFunc<T extends TestIndex>(t: T): void;
 declare function testFuncStrict<T extends TestIndexWithStrict>(t: T): void;

Consumer code

testFunc({
 test: {
 // Compiler doesn't see properties here
 }
});

testFuncStrict({
 test: {
 // Compiler see a?, b? and c
 }
});

Expected behavior:
Completion in testFunc({ test: { ... } });