Typescript WTF Moments 9: Evolving Empty Array Type

const a = false || []
//    ^?
const b = []
//    ^?
function c() {
//       ^?
  return []
}
const d = c()
//    ^?

let b = false || []
//  ^?
const a:number[] =  b
const c:string[] =  b

b = a // error as expected
b = c // expect as expected


let b1 = []
//  ^?
const a1:number[] =  b1 // did not expect error but error
const c1:string[] =  b1 // did not expect error but error

b1 = a1 
b1 = c1 

// with type annotation
let b2:any[] = []
//  ^?
const a2:number[] =  b2 
const c2:string[] =  b2 

b2 = a2 
b2 = c2