Yes, at least it's worth looking at the log file. I expect to find hints on whether the snapshot reverts at startup or after powering off the VM as well as the reason for this behavior. It will also be helpful to monitor the VM's files. Please take some screen shots of the VM's datastore folder before powering on, while powered on and after powering off the VM to see what changes. Make sure you refresh the datastore browser window before taking the screen shots and resize the datastore brower window to see al the details (sizes, time stapms, ...).
André