virtualbox.org

I installed a package that set a HOME enviroment variable, which led to VirtualBox ignoring the value of defaultMachineFolder in VirtualBox.xml, and always using the HOME directory for .VirtualBox and "VirtualBox VMs". I think that's undesirable behavior.

That environment variable has a very specific name, so it's not by coincidence that the value was changed.
Shouldn't you report this to the package maintener instead, if this is undesired?

I'm not aware that VBox uses a HOME env variable. The variable with that behaviour is called VBOX_USER_HOME, and there's no way some unrelated package chose that.