Regression in nightly build use of `this` type?

[myitcv]

Easiest explained via the repro steps:

$ cd `mktemp -d`
$ npm init --force
$ npm install --save-dev typescript@2.2.0-dev.20161122
$ grep -r 'onload:' node_modules/typescript/lib/
node_modules/typescript/lib/lib.es6.d.ts:    onload: (this: this, ev: Event) => any;
node_modules/typescript/lib/lib.es6.d.ts:    onload: (this: this, ev: Event) => any;
node_modules/typescript/lib/lib.es6.d.ts:    onload: (this: this, ev: Event) => any;
node_modules/typescript/lib/lib.es6.d.ts:    onload: (this: this, ev: Event) => any;
node_modules/typescript/lib/lib.es6.d.ts:    onload: (this: this, ev: Event) => any;
....

But then

$ npm install --save-dev typescript@2.2.0-dev.20161124
$ grep -r 'onload:' node_modules/typescript/lib/
node_modules/typescript/lib/lib.es6.d.ts:    onload: (this: Document, ev: Event) => any;
node_modules/typescript/lib/lib.es6.d.ts:    onload: (this: HTMLBodyElement, ev: Event) => any;
node_modules/typescript/lib/lib.es6.d.ts:    onload: (this: HTMLElement, ev: Event) => any;
node_modules/typescript/lib/lib.es6.d.ts:    onload: (this: HTMLFrameElement, ev: Event) => any;
node_modules/typescript/lib/lib.es6.d.ts:    onload: (this: HTMLFrameSetElement, ev: Event) => any;
node_modules/typescript/lib/lib.es6.d.ts:    onload: (this: HTMLIFrameElement, ev: Event) => any;
...

This has the obvious impact:

let image = new Image();

// with typescript@2.2.0-dev.20161122
image.onload // has type HTMLElement.onload: (this: HTMLImageElement, ev: Event) => any

// with typescript@2.2.0-dev.20161124
image.onload // has type HTMLElement.onload: (this: HTMLElement, ev: Event) => any

Is this an intentional change?

[myitcv]

@mhegazy et al - any thoughts on this?

[myitcv]

@mhegazy I'd like to be able to get back to using the latest nightly, help to flush out issues on your side and ours. But because of this issue, the nightly build is broken from our perspective.

Do you have any indication on when this will be fixed?

Or are there bigger question that arise out of #12433 that need addressing/thinking about first?

Thanks

[mhegazy]

i need to update the script that generates the file in https://github.com/Microsoft/TSJS-lib-generator. I have not had a chance to do that. PRs are always welcomed.

[myitcv]

@mhegazy this bug is present in the now released 2.1.4 and 2.1.5.

One thing I'm not clear on is why this isn't breaking for more people?