Fatal trap 9 when rebooting after installkernel on VirtualBox VM

Hello.

I'm tracking head with VirtualBox VM. Everytime new snapshot is
released I update to same revision. So buildworld, buildkernel and
installkernel always completes sucsessfully. But when rebooting system
always crashes with 'Fatal trap 9: general protection fault while in
kernel mode' message. And I closed VM window and restart VM, new
kernel start up without any problem.

https://www.utahime.org/FreeBSD/VirtualBox_FreeBSD_12.0-ALPHA3.png

This is a screenshot of latest update (ALPHA3 -> ALPHA4).

Does anyone else experienced it?

Conditions about VM and host are following:

VM:
  CPU: x4
  Memory: 8GB
  Disk: 100GB SATA
Host:
  CPU: Intel Core i7 4770S
  Memory: 16GB
  Disk: 2TB SATA
  OS: 64bit Windows 10 Enterprise 1803

Best Regards.

---
Yasuhiro KIMURA