Ok, as said in the comments I've reproduced the issue.
It arises using the current codeline of Q2A-SEO-links, and it's not due to the CKEditor4 plugin.
Solutions :
1) (quick&dirty)
temporarily remove the Q2A-SEO-links plugin from your
[q2a-root]\qa-plugin\
folder
(and wait for a patch for it)
2) apply the following patch (that I've used and seems to work in my test-case) :
change this line inside the qa-seo-links.php file
from :
$safe = preg_replace('/^<!DOCTYPE.+?>/', '', str_replace( array('<html>', '</html>', '<body>', '</body>'), array('', '', '', ''), $dom->saveHTML()));
to :
$safe = preg_replace('/^<!DOCTYPE.+?>/', '', str_replace( array('<html>', '</html>', '<body>', '</body>'), array('', '', '', ''), html_entity_decode($dom->saveHTML(),ENT_QUOTES,'utf-8')));
In my test case it solves the problem.
However keep in mind that I'm not the developer of the plugin ( nor I'm a php developer ! 
).
So the right way in both cases should be that of waiting for the official patch
EDIT :
deleted the previous instruction :
$safe = preg_replace('/^<!DOCTYPE.+?>/', '', str_replace( array('<html>', '</html>', '<body>', '</body>'), array('', '', '', ''), html_entity_decode($dom->saveHTML(),ENT_QUOTES,$encod)));
(see the comments below)
