I'm running Ubuntu Trusty using the current version of VirtualBox from Oracle's repo (with the extensions, if that matters).
When I create a Debian Wheezy guest using UEFI mode, the install works fine and the first boot is successful after the install. I then powered it off via the "poweroff" command, cloned the VM using the VirtualBox GUI.
After this point, the machines will not boot, neither the original or the clone. When I power them on, I get the VirtualBox EFI shell rather than GRUB.
The required EFI partitions are certainly present (the machine will boot at least once) so I know that's not an issue, which also rules out issues like "GRUB not being installed".
I would like these machines to be bootable, but I'm more curious as to why cloning a VM in UEFI mode prevents the original machine from booting. I could possibly see disk UUIDs changing affecting a clone, but I'm baffled as to why the original machine also won't boot.