OpenBSD: After reboot, cannot get past installation program

openbsd_install_problem.md

I am trying to install OpenBSD/amd64 5.9 inside VirtualBox 5.1. I did this successfully with FreeBSD 10.3 last weekend, so I had high hopes for success with OpenBSD. Since the FreeBSD install required a .iso file, I located a similar file for OpenBSD:

http://ftp5.usa.openbsd.org/pub/OpenBSD/5.9/amd64/install59.iso

The installation process went fairly smoothly. I selected a root password and created one user and that user's password. I selected the defaults in almost all cases and attempted nothing fancy. I finally got to this point:

CONGRATULATIONS! Your OpenBSD installation has been successfully completed.
To boot the new system, enter 'reboot' at the command prompt.

So I then entered reboot at the # prompt, and the system proceeded to reboot in what appeared to be the expected manner. However, after the demsg message printed out and I got to here:

root on rd0a swap on rd0b dump on rd0b
erase ^?, werase ^W, kill ^U, intr ^C, status ^T

... the system immediately returned me to:

Welcome to the OpenBSD/amd64 5.9 installation program

... and presented me with the same Install, Autoinstall, etc. choices as before?

I've now gone through the installation process 3 times and have never gotten to a login prompt. What am I doing wrong?

On freenode #nycbug, bcallah came to my rescue. He asked if I had removed the ".iso" file from the VM. I had not. This meant that reboot tried to reboot from the .iso file.

I then went to the main VirtualBox window. Down at the bottom there is (or was) a row of icons. The second of those icons indicated that the .iso file was present. By clicking, I was able to, in effect, eject it. Thereafter rebootDWIMmed.