We've had this problem since upgrading to Horizon 7.13.1, and it still carries over to the more recent 8.x releases. We used to be able to go in and edit the settings of a desktop pool (full clones) without the template being present. We sometimes clear our template inventory in order to ensure the next provisioned machine will require a fresh re-templating of the master image, but aren't necessarily re-templating that master image right away. The pool may not get any action for several months, but if we want to go in and edit any other characteristic of the pool, it will not allow those settings to change without the presence of the associated template. Used to be able to do this on prior versions of Horizon, but this a very frustrating change. Seems like there should be some way to bypass the check for the template if I'm just making a superficial change that isn't requiring any provisioning within the pool.