iliasn, I checked it on Plesk 11.5.27 - it works without any problems. I will check it on 11.0.9 too.
I used next steps:
1. install Plesk 11.5.27
2. create subscription with domain "kriogen.tld"
3. check that vhost.conf and vhost_ssl.conf are absent in main configs (conf dir was relocated to system dir in Plesk 11.5)
[root@ppu11-5 ]# grep -R .conf /var/www/vhosts/system/kriogen.tld/conf/last_httpd.conf | grep Include
[root@ppu11-5 ]#
4. create vhost.conf and vhost_ssl.conf files in the same directory (we support only these names)
[root@ppu11-5 ]# ls /var/www/vhosts/system/kriogen.tld/conf/ |grep vhost
vhost.conf
vhost_ssl.conf
[root@ppu11-5 ]#
5. reconfigure domain
[root@ppu11-5 ]# /usr/local/psa/admin/sbin/httpdmng --reconfigure-domain kriogen.tld
6. check that files were added to main config
[root@ppu11-5 ]# grep -R .conf /var/www/vhosts/system/kriogen.tld/conf/last_httpd.conf | grep Include
Include "/var/www/vhosts/system/kriogen.tld/conf/vhost_ssl.conf"
Include "/var/www/vhosts/system/kriogen.tld/conf/vhost.conf"
[root@ppu11-5 ]#
Do you use the same steps?