Thanks for the report. This is a regression introduced in 6.1.4 which
affects all hosts. As @nycnewman reported in #19490 this is a problem
in the VirtualBox GUI and as reported here is also reproducible if
running 'VBoxManage unregistervm VMname --delete' of a VM while the GUI
is running.
The easiest way to reproduce this on the command line is the following
which works for me when there are no other VMs created:
$ VirtualBox &
$ VBoxManage createvm --name fubar --register
$ VBoxManage unregistervm fubar --delete
[1] + Memory fault(coredump) VirtualBox
