Discriminated union narrowing fails when use template literal types as tag

TypeScript Version: 4.2.0-dev.20201211

Search Terms: narrowing, discriminated union, template literal types

Code

type Types<T extends string> = {
  one: `${T}/one`;
  two: `${T}/two`;
}
type OneObj<T extends string> = {
  type: Types<T>["one"];
  one: string;
}
type TwoObj<T extends string> = {
  type: Types<T>["two"];
  two: string;
}
type OneOrTwoObj<T extends string> = OneObj<T> | TwoObj<T>

declare function acceptsOneObj<T extends string>(oneObj: OneObj<T>): void;
declare function acceptsTwoObj<T extends string>(twoObj: TwoObj<T>): void;

function f<T extends string>(oneOrTwoObj: OneOrTwoObj<T>, types: Types<T>){
  switch(oneOrTwoObj.type){
    case types.one:
     return acceptsOneObj(oneOrTwoObj); // Error: Argument of type 'OneOrTwoObj<T>' is not assignable to parameter of type 'OneObj<T>'.
    case types.two:
     return acceptsTwoObj(oneOrTwoObj); // Error: Argument of type 'OneOrTwoObj<T>' is not assignable to parameter of type 'OneObj<T>'.
  }
}

Expected behavior:
oneOrTwoObj should be narrowed to OneObj or TwoObj in function f

Actual behavior:
narrowing fails

Playground Link:
playground

Related Issues:

Start with the linked TypeScript Playground reproduction and the generic function f, focusing on how the switch over oneOrTwoObj.type handles template literal types. Confirm the current behavior, then trace the type-checking path for discriminated-union narrowing. Done means each switch branch narrows oneOrTwoObj to the corresponding OneObj or TwoObj so the acceptsOneObj and acceptsTwoObj calls type-check.