It happened in our test loops with the optin -no_shutdown. The shoudown loop with/without this option is different, but as we are not handling the vm object in env in a right way the script try to connect to the monitor after the qemu-kvm process already quit which cause problem in the following cases in a test loop. So if you want to change the vm parameters you need at least update the object in env. And that's maybe a little complex so I suggest that we need a common use function for this. And the method that start a vm inside test cases have some problem we can just force on a piece of code not change them one by one.