Broken out from bug 5870.
In Web Admin's Agent page, when pressing ENTER after modifying agent_hostname or xserver_args, it tries to stop the vsmagent service.
Similarly, when changing allowed_groups, allowed_shadowers or max_sessions_per_user on the Master page, when pressing ENTER it tries to stop the vsmserver service.
The expected behavior would be to save the changes.
The solution likely involves having separate <form> elements for the service-parts of these two pages.
Furthermore, when pressing ENTER in the popup, it tries to delete the item and you most likely end up with the error for not checking the confirm box.
When multiple submits are present in a form, the browser will use the first submit-button. The issue with the popup case is that the delete-button comes first in the HTML.
A possible solution for the popup issue with ENTER is to reorder the Delete/Save buttons in the code but keep their visual positions as-is using CSS.