Virtualbox hang problem

A VM just froze and wouldn't close so I had to force it, but the VBox GUI thinks it's running even when I close it.

I manually killed the related process by doing ps aux|grep VirtualBox and found the PID 6191

I killed it with "kill -kill 6191" but it remains open and as "defunct" so I can't restart it because the GUI freezes when I click on it because it thinks it is running still

 6191  5.2  0.0      0     0 ?        Zl   09:31   0:53 [VirtualBox] <defunct>

After several minutes the process disappeared but there's no way that I know to instantly solve this issue.  Even killing the GUI doesn't fix it, the only way would probably be to restart the entire service, thus killing your other VMs at the same time.