Greetings,
I took a quick look at the log files and the server is sending emails for submitted build requests. Here is one example and perhaps this information can assist is identifying who is actually submitting of the requests:
Jul 07 09:54:15 localhost live-build-cgi: add web build (20130707.095415.783039348) from 71.211.232.159.
Jul 07 09:54:15 localhost live-build-cgi: options 20130707.095415.783039348 |email
john.crout@gmail.com|binary_images iso|distribution wheezy|config standard|cgipackag
es |architectures amd64|archive_areas main|chroot_filesystem squashfs|linux_flavours 686-pae|security true|apt_indices |bootappend_install |bootappend_live |bootloader
syslinux|debian_installer true|iso_application Debian Live|iso_preparer live-build;
http://packages.qa.debian.org/live-build|iso_publisher Debian Live project; http:/
/
live.debian.net/;
debian-live@lists.debian.org|iso_volume Debian Live 20130707-06:46|memtest none|net_path /srv/debian-live|net_server 192.168.0.1|source_images tar|s
ources false