Why is TypeScript unable to infer the type properly?

Question

I have two examples where TypeScript type inference is not working as I expect it, maybe these two are related, maybe it's a TS bug, maybe I am only too dumb to understand it.

Example #1

interface AType {
  type: 'A'
  message: string
}

interface BCType {
  type: 'B' | 'C'
}

type Test = AType | BCType

function doSomething(test: Test) {
  if (test.type !== 'B' && test.type !== 'C') {
    test.message
  }
}

The test.message gets the error

Property 'message' does not exist on type 'Test'.
  Property 'message' does not exist on type 'BCType'.ts(2339)

Why isn't test of AType now, so it has a message property? If I remove the 'C' from the type, it works. If I check for === 'A', is also works.

Example #2

interface AType {
  type: {
    id: 'A'
  }
  message: string
}

interface BType {
  type: {
    id: 'B'
  }
}

type Test = AType | BType

function doSomething(test: Test) {
  if (test.type.id === 'A') {
    test.message
  }
}

Same here:

Property 'message' does not exist on type 'Test'.
  Property 'message' does not exist on type 'BType'.ts(2339)