Collectd codec and notifications

I am attempting to use collectd to monitor various stats on many linux hosts. All the stats are sent to logstash via UDP and the collectd logstash codec. All worked great and I can see all my stats/hosts in kibana.

I have now configured collectd to send notifications if, for example, load is to go above a certain threshold. If I disable the collectd codec in logstash and divert to stdout I can see all these notifications (in the collectd binary format, with a clear text notification string). With the codec enabled all stats get through but the notifications appear to be dropped, with no acknowledgement of their existence.

Has anyone else had any luck with collectd notifications into logstash? Does the codec simply not support notifications? Or is this a bug?