I'm not sure we've seen this problem with a xenial guest. However, I did regression test and verify that xenial guests still boot in secureboot mode w/ the shim-signed package in -proposed:
ubuntu@ubuntu:~$ dpkg -l | grep shim-signed ii shim-signed 1.33.1~16.04.9+15.4-0ubuntu5 amd64 Secure Boot chain-loading bootloader (Microsoft-signed binary) ubuntu@ubuntu:~$ sudo mokutil --sb-state SecureBoot enabled
I'm not sure we've seen this problem with a xenial guest. However, I did regression test and verify that xenial guests still boot in secureboot mode w/ the shim-signed package in -proposed:
ubuntu@ubuntu:~$ dpkg -l | grep shim-signed 16.04.9+ 15.4-0ubuntu5
ii shim-signed 1.33.1~
amd64 Secure Boot chain-loading bootloader (Microsoft-signed binary)
ubuntu@ubuntu:~$ sudo mokutil --sb-state
SecureBoot enabled