alert configuration question: why did it trigger?

Here is the Trigger Condition:

• The node is indeed down.
• Its custom property "node_tier" was set to 3.
• The alerts are designed to only fire when that value is between 1 and 4.
• I wanted to disable the alerts and so I set "node_tier" to 5. The moment I saved it, the alert got triggered again:

Tier 5 node Node_ABC is Down.

 

Additional Information:

- Node Tier: 5

- Alert: [DATG-DM-VO] node down, Tier 3 escalation: email once a day

   Trigger Count: 1

   Trigger Time: 11/3/2014 4:04:40 PM

   Acknowledgement: Not Acknowledged

Here is the alert. Note that the "Name of Alert" matches "Alert" value above. It is the same alert. "Trigger time" matches the time the node went down, "Trigger Count" seems wrong: the alert already fired once before this one, just when it happened.

Why did this alert fire?

Thanks!