A Strange VirtualBox Quirk
I also run the same VM on my laptop. No such font quirk.
I tried other VMs and they all showed a different font in the VM window.
I tried many things, including a fresh /home directory, restoring from backups before the system merger, and searching for differences in config files. Nothing.
I wondered what was different between the two computers. There was one difference. The office system auto-started one headless VM during the system boot. I inherited that VM from the retired server. With the server I rarely ran a desktop.
I disabled the auto-start on the office system and rebooted. The fonts were normal in any VM window I started.
I rebooted. I logged into the desktop, manually started the headless VM, and started a different VM. No font quirk.
I restored the auto-start but added a 120 second delay. Plenty of time to finish the boot sequence and log in. The fonts again were different in the encrypted VM window.
I tried starting the VM headless from a terminal window. Different fonts.
Apparently VirtualBox uses a default font when auto-starting VMs from outside of X. As most people run headless VMs on headless servers where X is not running, most people never would see this anomaly.
The quirk is mildly annoying but not a bug.