TypeScript Generics ignore extend types

generics-ignore-extend-types.ts

abstract class A<T1, T2> {

}

class B extends A<string, number> {

}

interface AClassStatic<T1, T2, T3 extends A<T1, T2>> {
    new (): T3
}

function getFromAClass<T1, T2, T3 extends A<T1, T2>>(aClass: AClassStatic<T1, T2, T3>): { t1: T1, t2: T2 } {
    return <any>{}; // dummy
}

const param = getFromAClass(B); // expect: {t1: string, t2: number}, actual: {t1: {}, t2: {}}