In particular:

:

Virtual machine pools are stateless by default, meaning that virtual machine data and configuration changes are not persistent across reboots. However, the pool can be configured to be stateful, allowing changes made by a previous user to persist. However, if a user configures console options for a virtual machine taken from a virtual machine pool, those options will be set as the default for that user for that virtual machine pool.

NOTE

Virtual machines taken from a pool are not stateless when accessed from the Administration Portal. This is because administrators need to be able to write changes to the disk if necessary.

"

And also

with

"

Ensure the virtual machine has a status of Down; you cannot detach a running virtual machine.