Anybody know how to resolve this known problem with Sun's VirtualBox?

[struggle4progress]

Under some circumstances, a virtual machine powers off correctly, but VB does not close the session. The result is that one has a machine powered off -- but since the session is still open, none of the settings can be changed, the description can't be edited, and the machine can't be restarted

In a websearch, the only solution I found was to shutdown all VMs, then quit and restart VB. This is a nuisance if there are one or more VMs one isn't really ready to shutdown

[struggle4progress]

1. This might be something like a spinlock issue: I have a VM running and shut down

several others, two of which powered off correctly but did not close session. Several hours later, the first powered-off machine has spontaneously closed its session, though the other still has an open session

[struggle4progress]

2. VirtualBox didn't completely quit, due to the open session: I had to force-quit

it, and on relaunch the powered-off but open-session machine reported it had been aborted