cron jobs in guest executing on host instead?

[groovix]

I am still trying to debug further and gather more details, but this has happened on two different installs now with different guest environments: VirtualBox 3 on Ubuntu 8.04 HOST running Ubuntu 9.04 GUEST, and Ubuntu 9.04 HOST running Ubuntu 9.04 as a GUEST. All are 32-bit on an AMD socket AM2 processor. My guests have a cron job set for 2 AM that warns via a zenity gui that the machine is going down and then reboots the machine, and about once a week in the morning the HOST has rebooted. At first I thought the guest reboot was triggering some host overheating or other problem leading to a host reboot, so I set the reboot for another time and got it to happen in front of my eyes once. I actually saw the zenity gui come up TWICE: I'm guessing one was on the guest and one was on the host, and then the host rebooted. It doesn't happen all the time and it doesn't seem to happen if the cron job was rescheduled after the guest has booted up.

There is definitely not any sort of reboot procedure in the host's cron.

My first and second instincts were that I was mistaken, but I'm getting pretty confident that VirtualBox has a pretty severe flaw in it. Before I go crazy trying to debug this I'm hoping someone else has seen this behavior.

Has anyone else had a problem with cron jobs or any other sort of program from a GUEST system mistakenly executing on the HOST?

[vbox4me2]

I can imagine the Host and Guest share a common user that have the same password, at some point the reboot signal is send to the Host, or a Guest is not rebooting properly and causing an unseen crash causing the Host to reboot.

[groovix]

I can imagine the Host and Guest share a common user that have the same password, at some point the reboot signal is send to the Host, or a Guest is not rebooting properly and causing an unseen crash causing the Host to reboot.

It has not happened since my last post. There are no common usernames between the guest and the host. Once a guest "shutdown -h now" in a crontab made the host shutdown instead of rebooting (usually the guest crontab has a "shutdown -r now"), so it really seems like it was executing the actual command on the host. I'm keeping my fingers crossed, maybe some Ubuntu security update happened to fix the issue.