Been keeping up to date with trunk and now a previously working error-decoration stopped working.
The error is added to the correct control, by id. The error is visible under h:message.

To support a newline under the entry the following mechanism is added, which also evaluates correctly to true. Thus the only error
seems to be inside the taglib that is

<h:message />

<h:panelGroup rendered="#{not empty facesMessages.currentMessages}">
   <br />
   <h:message for="nameOfControl" errorClass="facesError" />
</h:panelGroup>

Removing the panelGroup does nothing. The message just won't show inside the h:message.
The error exists, and is as far in as I step correctly added to StatusMessages:keyedMessages by its correct id.

/K