Because JSF supports sets and arrays natively, but not Sets - Seam does some trickery there. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4054243#4054243 Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&p=4054243