I had to dive into this for a while to understand why this is happening. I THINK this is a bug. I'm not 100% sure because there is an explicit check that handles this kind of situations. However, that could have been from older versions of Q2A and Gideon forgot to update it too. So not sure.
The issue comes from this function: https://github.com/q2a/question2answer/blob/v1.6.3/qa-include/qa-app-format.php#L1310 . For some reason, the URL is built from "scratch" by using the qa_path_to_root() function.
This is how I think that function should have been written, if I'm not missing anything:
Return the url for $page retrieved from the database
return ($page['flags'] & QA_PAGE_FLAGS_EXTERNAL) && (strpos($page['tags'], '://') !== false)
Give it a try.