[Chrome] @grant not none causing page JS issues

[Mottie]

The following conditions appear to cause an issue and somehow break JS code on a page:

• Setting the @grant to anything other than none.
• Accessing the document from within a userscript.
• Strict CSP (e.g. GitHub)? Just guessing here...

Several issues were reported that GitHub repo project card drag and drop was no longer working with a userscript. No JS errors are seen.

• Can't move cards on "Projects" from one column to another StylishThemes/GitHub-Dark#581
• Can't move Github Project cards when GitHub code show whitespace is active Mottie/GitHub-userscripts#36

After some investigation, I found that numerous userscripts were causing the problem. Eventually I found that this minimal userscript would break the project card drag and drop, but only in Chrome.

// ==UserScript==
// @name        test
// @version     1.0.0
// @include     https://github.com/*
// @grant       GM_addStyle
// ==/UserScript==
console.log(document.readyState);

Changing the @grant to none, or not accessing the document will not cause the aforementioned problem.

This issue appears to occur only in Chrome in both TM 4.5 and TM Beta 4.6.5694. Firefox does not have this issue. I did not test other browsers or older versions of TM.

I've tried to investigate the cause, but GitHub has three minified JS files which are difficult to navigate.