Occasionally an escalation will appear to get "stuck" in an active state even after the trigger associated with it has long since recovered. Most commonly, this results in continual emails/alerts from Zabbix even though there is no longer a problem. The only way that I've found to resolve it is to delete the row in the escalations table for that escalation. Another user reported to volter in #zabbix that they fixed it by disabling and then re-enabling the associated trigger.
I have not seen this issue for myself in quite a while, but I have seen it come up #zabbix on freenode several times.