Just installing... Pre-Installation 2/4 - point 4 says root config.php is "writeable", yet it's attributes are -rw-r--r-- (writeable only for the owner).
"Warning: config.php needs to be writable for OpenCart to be installed!", when I clicked continue.
But admin/config.php also had attributes as above and rightly so said "Unwritable". And it changed upon chmod & refresh - as expected.
Summary: correct W indicator for admin/config.php; but WRONG W indicator for root config.php.