I've been getting frustrated with something causing focus to change during page load and have tracked it down to Rangy.

When you refresh a page with an mform, if you select a basic text element and start typing into it, the focus is lost when Atto loads.

Looking into it further I've tracked this down to rangy.

To track this down, add the following code just inside the closure for lib/amd/src/first.js:

$('*').on('focus blur', function(event) {debugger;});

Open a form page (I used add new forum) and click in the first text box as soon as the page loads as early as possible

I can be typing something and suddenly the focus jumps.

This seems to be coming from Rangy's feature detection and specifically from this line: https://github.com/moodle/moodle/blob/master/lib/editor/atto/yui/src/rangy/js/rangy-textrange.js#L100