This bug is identical to Bug 195458. I run a bunch of FreeBSD VMs on a FreeBSD 11-1R host using VirtualBox in Headless mode (using standard RC scripts). Historically I was running FreeBSD 10R on my VMs and they would shutdown when the command was issued. I updated a couple of months ago via source to 11-1R and now when I the "acpipowerbutton" command is issued they hang as per the above bug. I just performed a fresh install of FreeBSD 11-1R on a newly configured VM and the issue is present. Please advise what details/configuration files you require to assist in resolving.
Running "shutdown -r now" in the VM reboots as expected. Running "shutdown -p now" also hangs the VM.
I'm thinking this is actually a VirtualBox issue as I just tested a CentOS VM and it is doing the same thing. The VBoxHeadless process doesn't terminate.