Enterprise Manager Metric Extension generates Event, but no Incident

I'm experimenting with Metric Extensions in a Enterprise Manager Cloud Control. I created 3 extensions.

Two of them have a threshold on a numerical column. These two work exactly as expected. If the value rises above the warning threshold, a warning event is created. This then causes a warning incident to appear.

The third extension is a bit more complicated and uses an SQL statement that calculates the state of the metric directly. So the column with the "threshold" is a string column that contains the strings "WARNING" or "CRITICAL" with these two word set as warning and critical trigger-values.

The problem is, when ever the SQL statement contains lines with these words I can see events being generated for them. But: No incidents.