i had a similar issue. On my system the line in bold caused the issue:
php_admin_flag safe_mode Off
Alias /error/ "/var/www/web5/web/error/"
ErrorDocument 400 /error/invalidSyntax.html
I just wonder why this happend. It was the first Domain. Seems it happens after installing version 2.2.12.
After i removed that line httpd -t returns "Config OK", but still no new vhosts are added to the file.
(I deleted an existing web, removed it from trashcan and recreated it - still no new entry. However teh timestap of the vhost config file changed, so "something" happend.)