Thank you guys for pointing me into the right direction. Problem was that there is no httpd.conf file on my cubian/debian. Thanks to this wiki entry http://wiki.apache.org/httpd/DistrosDefaultLayout I found out where to look for the configuration. And in fact there was a listen 8888 in the ports.conf file. I commented that out and my btsync gui is available again! Sorry for the stupid quesion: If the gui is not running on apache - where is it comming from?