function discards outer type-check on union type

[MrAndersen1]

TypeScript Version: 2.2.0-dev.20170113

Code

class test1 {
	someProp;
}
class test2 {
	anotherProp;
}

let myTest: test1 | test2;
if (myTest instanceof test1) {
	// valid
	myTest.someProp;

	// invalid, someProp does not exist on type 'test2'
	() => myTest.someProp;

	// meaning if you have a eg. forEach
	[].forEach(() => {
		// you will need an instance check here too
		// invalid
		myTest.someProp;

		// valid
		if (myTest instanceof test1)
			myTest.someProp;
	})
}

Expected behavior:
I expected typescript to know myTest was instanceof test1 inside the function. It did not give these errors in typescript 1.8

Actual behavior:
It lost this knowledge inside the function.

[HerringtonDarkholme]

Possible duplicate of #9998

[RyanCavanaugh]

#9998 / #11498

[MrAndersen1]

Ah, yes, probably. My search for similar issues was not good enough it seems. Thanks!
Interesting read.