Steps to reproduce the issue

Create redirect in Redirect Manager
Expired URL: http://www.domain.com/some-url
New URL: http://www.domain.com/some-new-url

Expected result

Entering http://www.domain.com/some-url in the browser address bar causes a redirect to http://www.domain.com/some-new-url

Actual result

Entering http://www.domain.com/some-url causes a redirect to http://www.domain.com/some-url/https://www.domain.com/some-new-url and throws a 404

System information (as much as possible)

Joomla 3.8
PHP 7.0.23
Force SSL: Entire Site
Search Engine Friendly URLs: Yes
Use URL Rewriting: Yes

htaccess:
RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} ^domain.com [NC]
RewriteRule ^(.*)$ http://www.domain.com/$1 [L,R=301,NC]

Additional comments

Workaround:

When New URL is set to just /some-new-url, it works.

Expired URL: https://www.domain.com/some-url
New URL: /some-new-url
Properly redirects to http://www.domain.com/some-new-url

I thought this was related to the 3.8 upgrade but it also happens on a few 3.7.5 websites that I've tested.

Is this expected behavior?

Joomla's documentation states:
"The Source URL you specify when you create the redirect should be the full URL as you would type it in your web browser."
"The Destination URL you specify when you create a redirect must be the full URL as well."