Comment # 11 on bug 1202851 from David Boyd

The user expectation is that when he/she reboots the VirtualBox VM guest, the
previously attached USB device is still attached.  This "Aborted" condition
detaches the USB device and after restarting the VirtualBox VM guest, the user
must remember to reattached the USB device.

Most of these users never shutdown the VirtualBox VM guest(s).

The problem is annoying to me, but I'm not the user who's scheduled backup
didn't run because there was no USB device available.