Steps to Reproduce:
1. Have a few managed hosts registered to a Sat 6.7 server
2. Go to Hosts->Provisioning templates page and create a clone of a template. I have used the "Kickstart default" template.
3. Check that template can be correctly previewed. You need a managed registered host for this.
4. Make the template invalid and unrenderable. The easiest way to achieve this is to make a typo in the name of a snippet to be included in the template. I have modified the line 245 of the template, adding an extra 's' to the 'remote_execution_ssh_keys' snipet name.
5. The change correctly activates the "Change" pane of the editor.
6. Go to the "Preview" pane of the editor. Use the "Preview is Outdated..." button if necessary. You will get an error, as the template cannot be rendered at the current state. Do not close the error widget.
7. Go back to the editor pane, and fix the typo (remove the extra "s"). The "Changes" pane will be correctly disabled, as there is no change in the template now. You can close the error widget now.
8. Go to the "Preview" pane. There is still a message "Error during rendering, Return to Editor tab." in the preview area, even if the template is already fixed. There is no "Preview is Outdated..." button to refresh the preview, and you are not going to get any preview.

Preview is not available, even if the template is correct and renderable

Expected results:
If the template is correct, a preview is always available, or at least the "Preview is Outdated..." button is available to do a manual refresh.