When going to "Monitoring", "Triggers" and selecting "Show only problems", "Show unacknowledged (7 Days), Min severity "High", for some hosts ALL triggers within this severity range are shown as "Acknowledged". The status is "OK". First of all I would expect acknowledged triggers not to be shown, but second these triggers have never been acknowledged (and don't show as such in the overview). So this appears to be a bug.
Running 1.8.2
Running 1.8.2