Fileupload nao atualiza imagem

<p:outputPanel id="dialogLogo">
					<p:dialog widgetVar="dlgLogo" modal="true" id="listaImagem" header="Logomarcas" height="400" width="700" style="font-size:11px">
		   	  		 		<p:messages id="msgImagem"/>
				   	  		 <p:panel header="Logomarca">
			  	  		 			<h:panelGrid columns="2">
				   	  		 		<h:outputText value="Selecione a Logomarca: *" />
				   	  		 		
				   	  		 		<p:fileUpload fileUploadListener="#{cadastroController.fileUploadAction}"   mode="advanced" update="idarquivo" process="@this"  sizeLimit="100000" allowTypes="/(\.|\/)(gif|jpe?g|png)$/"></p:fileUpload>
				   	  		 		
				   	  		 		&#65279;Arquivo selecionado: &lt;h:outputText id="idarquivo" value="#{cadastroController.nomeArquivoSelecionado}"/&gt;<br/> 
			  	  		 			&lt;/h:panelGrid&gt;  
				   	  		 &lt;/p:panel&gt;
				   	  		 &lt;p:fieldset&gt;
				   	  		 	&lt;center&gt;
				   	  		 		&lt;p:commandButton value="Atualizar" onclick="dlgLogo.hide();" update="formPrincipal:imagem"/&gt;
				   	  		 		&lt;p:commandButton value="Fechar" onclick="dlgLogo.hide();"/&gt;
				   	  		 	&lt;/center&gt;
				   	  		 &lt;/p:fieldset&gt;
				   	  	&lt;/p:dialog&gt;
				&lt;/p:outputPanel&gt;