Duplication of notifications

Hi,
After upgrade to 3.1.3 notifications are unusable for a quite common use-case.
Notifications are now triggered if the filter rule is satisfied, regardless of whether a specific event was already in previous notifications or not.

In other words, if I had just 1 event in the stream (say security group change, for example), and my Event definition is configured as:
- Search within the last = 60 minutes
- Execute search every = 1 minute

I will receive 60 emails(!). This is completely impractical. There should be an option to make Graylog just send 1 notification for 1 event in the original stream.

We did not have this issue with previous Graylog versions.

* Graylog Version: 3.1.3