It seems that there are some problems of acknowledge in Monitoring -> Triggers screen.

1. All problem status triggers are have (1) acknowledge (screenshot1). However, the screenshot is immediately after installing zabbix server, and Zabbix server host enabled. In fact, click one of Acknowledge link, the ack message is empty(screenshot2)

2. Put a test message into ack textarea and press "Acknowledge & Return" button, then return trigger list screen. I cannot click "Acknowledged" (screenshot3). I think it's a little inconvenient, I or my co-workers may try to click to make sure of acked messages from trigger screen.

3. Go to Monitoring > Event screen, and show above ack message, "[ BULK ACKNOWLEDGE ]-" string in the ack message (screenshot4).