Wrong value type is accepted when key is accessed through an object

TypeScript Version: 4.3.2

Search Terms:

Code

enum TheKeys {
    k1 = 'k1',
    k2 = 'k2',
}

const someObj = { someProp: TheKeys.k1 }

const a: { [k in TheKeys]?: { prop: string }} = { [someObj.someProp]: 1 } // no error, but should be
const b: { [k in TheKeys]?: { prop: string }} = { [TheKeys.k1]: 1 } // error as expected

Expected behavior:
(To my understanding) the type error that's generated for b should be generated for a as well.

Actual behavior:
No error is generated for 'a'.

Playground Link:
https://www.typescriptlang.org/play?ts=4.2.3#code/KYOwrgtgBAKgFsA0sAngZygbwFBT1AawEYoBeKAcmIoBpd8CAmMyp27AX22wGMB7EGgAuUNHwjAA8gCMAVi0yjxwAAoAnPgAcAXLATJ0AOmJQuvAcKgBDXYoDaBKAEsQepKjQBdAPy2omjR1RITUXAHNTDgUoOzEJGVlDONVAz10SKIB6TKgQPihgNQ01GihpMBE0OD4wABsAEzLgc0ERaT8HZ1d4d3QfPwCtXWFQkAiOKPJ7HoM0YyI0qAyobIKivjVrDGAAD01gHiFgeqA

Related Issues:
None that I know of.

Start by reproducing the example in the linked TypeScript Playground using the reported TypeScript versions. Investigate how computed property keys from object properties are checked against mapped-type value requirements; done when the a example reports the same type error as b and the behavior is covered by a regression test.