I've got the same with 14.04 amd64.
I used hd-media boot.img with Easy2Boot USB hdd. There is a lot of images on (more than 10) disk, but installer fails to scan them. If I open console with Alt+F2, the partition with images already mounted in /hd-media like as AndreiF wrote. Mounting image to /cdrom doesn't help - installer tryes scan images again and all repeates.
I've got the same with 14.04 amd64.
I used hd-media boot.img with Easy2Boot USB hdd. There is a lot of images on (more than 10) disk, but installer fails to scan them. If I open console with Alt+F2, the partition with images already mounted in /hd-media like as AndreiF wrote. Mounting image to /cdrom doesn't help - installer tryes scan images again and all repeates.