Zabbix Server 2.2 works in UTC. Admin from USA creates maintenance period: click button "calendar" and "Now" - Time is set from USA timezone(current time from OS) and is not valid for maintenance now.
Zabbix frontend must use time from server.
Before in zabbix 2.0 fields "Active since" and "Active till" by default were from current server time and were not needed to edit. It related to "one time only" period too. Will be enough to make behavior "maintenance" though as zabbix 2.0