I have been doing some application testing using Hyper-V 6.1 virtual machines. I have Hyper-V installed on a Win 2008R2 server. I have three VMs configured and running with snapshots. Once I install the application and then revert back to a snapshot prior to the application install, one of my VMs works as advertised and does not have the application installed which is what I would expect and what I found in my original testing of the snapshot / revert functionality. The other two have all the changes I have made to the VMs back through all the snapshots all the way back to the original VHD file, which never had the application installed.
I would try to delete the snapshots trying to get back to an instance of the VM that did not have the application installed on it but I could not on two of my VMs. I eventually deleted all the snapshots so I was back to using the original VHD file (no avhd files left in the Virtual Hard Disks folder). Now the original VHD file had all the updates and changes that all the snapshots (avhd files) had. I know there is a way to purposely make the changes fold back into the original vhd file from the avhd files but I certainly did not attempt it.
How does this happen and how can I stop it?