adm.gui.php -> GUI -> "Dropdown first entry": All vs. None
Choosing the default All or None causes the first selection in hostgroup select boxes to only be either 'All OR None'. The behavior here should be the option of all or none, but to default to the setting.
Using "All" makes it very difficult to navigate to some hosts, filter, and search properly; however, the result is that some selections can include very large groups (or all) hosts managed by Zabbix (for large installations) this causes excruciatingly slow page loads (or timeouts). It would be sane to have a default of None if no context can be determined, but the option for the user to expand to All.