Not sure what you're adding in the <content-header:> param, but that's going to override the ENTIRE content of content-header. Example from pages.dryml.erb:
<def tag="index-page" for="<%= model.name %>">
<page merge title="#{ht '<%= model_key %>.index.title', :default=>[model.model_name.human(:count=>100)] }">
<body: class="index-page <%= model_class %>" param/>
<content: param>
<header param="content-header">
<h2 param="heading">
<ht key="<%= model_key %>.index.heading">
<model-name-human model="&model"/>
</ht>
</h2>
<p param="count" if>
<ht key="<%= model_key %>.collection.count" count="&collection_count">
<count summary/>
</ht>
</p>
</header>
--Matt Jones