Forgot to say, my duplicates are in a t:dataTable (plus jscookmenu support is broken). MyFaces and Tomahawk had ID generation 'compatibility issues' with JSF RI in the past, which https://issues.apache.org/jira/browse/MYFACES-1010 indicates needs a fix in the JSF RI. All this occured around the time Tomahawk 1.1.4 was coming out (as far as I recollect). A colleague also saw on some official Java site (cannot find link) which indicates that using a 'binding' attribute can cause 'issues' with duplicate IDs on the JSF RI 1.2 - my tables do define a binding. Dave View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4051973#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...