kyrios The reason you didn't had to reboot is because the usysconf trigger restarts the virtualbox service which does a "modprobe" to reload the virtualbox kernel module.
Sounds plausible. I removed everything for VBox (including in my home directory, and .config) and started over by installing virtualbox-current. Still created a Budgie VM without rebooting, but I'm assuming that the previous modprobe is still effective.
I'll experiment some more when I install this again on a machine for the first time.
By the way, every time I install VirtualBox I need to search through the menus to find the option to turn on snapshots. I can never remember how to do it, especially this time ... been looking for a while and still haven't found it. Do you remember how? I can remember what the setting looks like, but not where to find it.