• Entire page opens in the wikitext editor.

So I think this is expected. Option+Control+E (etc., the modifier keys depend on your OS and browser) is a shortcut for the "Edit source" article tab, rather than for switching editors. It just so happens that when you have the normal page editor open in visual mode, that will switch it to source mode, but it's not intended to switch modes in the reply widget or elsewhere.

• Since I use the 2017WTE, it gives me a little pop-up note to say that it's recovered my saved changes.

This isn't right, but what happens is actually different than what it looks like.

When you press Option+Control+E, and confirm that you want to "leave the site" (you should get a modal pop-up), the entire page reloads (this is the result of T244942).

Then the page editor loads – it does not actually recover any changes, as there isn't anything to recover. In the background, the reply widget loads too because you have an unsaved comment, and recovers your input in the reply widget. You can't see it because the page editor is open – but it still gets set up in the background, and it's the reply widget that displays that pop-up. If you close the page editor, you will see the reply widget with your comment intact.

I have to click the "Read" tab twice to get the 2017WTE to close, but the Reply widget does appear to still be there, with my comment still in it.

Although it eventually does the Right Thing with my comment, if you happen to know how to switch back, the process for getting to that point might set a new standard for "non-intuitive".