I can confirm this is still a problem with Jessie. Debian installer with preseed fails to automatically select the disk to install grub to (/dev/vda). This causes the installation to stop and wait for user input when building on QEMU / KVM: https://github.com/sammcj/packer-qemu-debian-jessie/issues/1 -- Sam McLeod @s_mcleod[https://twitter.com/s_mcleod]