Also, as Bjab pointed out in another thread addressing the same issue, not all file changes are reflected in the upgrade_changes.txt:

Originally Posted by Bjab
In the upgrade_changes.txt file (which I used to upgrade without re-modding my whole system) are not all changed files mentioned.

Files that should be added:

VERSION-7.5.7:CHANGED: admin/loginas.php
VERSION-7.5.7:CHANGED: libs/html.inc.php
VERSION-7.5.7:CHANGED: scripts/changebasic.inc.php
VERSION-7.5.7:CHANGED: scripts/logout.inc.php
I had the same problem myself, but adding the new changes in libs/html.inc.php fixed it for me.