Raven 2.1 : Customized error messages not working

I have raven 2.1 and Statamic 1.10.1 I have my custom messages set up in the formset.yaml and I use the ```{{ if {raven:has_errors} }} code block, given as an example in the docs here http://statamic.com/add-ons/raven/tags

Missing fields are shown with their fieldnames, but the ```{{message}}-part does not appear.

{{ raven:errors }}{{ missing }}
<li>{{ field }}: {{ message }}</li>{{ /missing }}

delivers just a list of missing fields, not my custom message.

Any thoughts why? Thanks Albert