thats not wordpress.
to your .htaccess and see if it goes away.
that will disable it for your entire domain, so if you would rather just disable it for stuff you do in the admin area, create an .htaccess (use notepad), put that code above in it .. and upload it to wp-admin/
if you just want to have certain files do this:
SecFilterSelective "REQUEST_URI" "/wp-admin/edit.php" "allow,nolog"
the above would go in the root .htaccess NOT in a /wp-admin one.
Or, lets say you want to post a word that might be typically blocked, like 'curl':
SecFilterSelective "POST_PAYLOAD" "curl" "allow,nolog"
Like before, that example would go in your main .htaccess
You can see the choices are many.