"editor.wordSeparators" option is not always honored

[nerdo]

• VSCode Version: Code 1.17.2 (b813d12, 2017-10-16T13:47:41.889Z)
• OS Version: Darwin x64 17.0.0
• Extensions:

Extension	Author (truncated)	Version
swift	Kas	0.0.3
php-namespace-resolver	Meh	0.8.0
material-icon-theme	PKi	2.2.3
vscode-intelephense-client	bme	0.7.2
vscode-eslint	dba	1.4.0
vscode-dash	dee	1.7.1
gitlens	eam	5.7.1
vscode-npm-script	eg2	0.3.1
phpunit	ema	2.1.1
LogFileHighlighter	emi	1.2.0
phpcs	ika	0.7.0
insert-cursor-at-beginning-of-each-line-selected	kai	1.0.1
prettify-json	moh	0.0.3
vscode-duplicate	mrm	1.2.0
debugger-for-chrome	msj	3.4.0
php-docblocker	nei	1.3.2
pdf	tom	0.2.0
vim	vsc	0.10.2

(4 theme extensions excluded)

---

Steps to Reproduce:

1. Set the editor.wordSeparators option to "editor.wordSeparators": "~!@#%^&*()-=+[{]}\|;:'",.<>/?". This is essentially the default value with $` removed.
2. Enter this in the editor

$this->stuff
this stuff
and $this thing

3. Place the cursor at the beginning of line 1 and press CMD+D to highlight the word $this. Nothing happens. Further, moving the cursor to anywhere within the word $this and pressing CMD+D highlights this, effectively ignoring the editor.wordSeparators.
4. Side note: using the mouse does seem to honor the setting.

Reproduces without extensions: Yes

[alexdima]

Duplicate of #15774