Primefaces Datatable Dialogue box issue - jsf-2

Question

I am using jsf 2.0 and primeface 3.5;
i am displaying a datatable and on the selection of any row, i display details in dailogue box. now the problem is when the page is loaded, and for the first time i select any row , the dialogue display nothing, but after that it works properly, what can be the reason of this issue
<h:body>
<h:form id="form">
<p:dataTable var="row"
value="#{user.list}" paginator="true"
rows="10" selection="#{user.selectedUser}"
filteredValue="#{user.filteredUser}" rowKey="#{row.attackID}"
rowsPerPageTemplate="5,10,15" selectionMode="single" paginatorPosition="bottom">
<p:ajax event="rowSelect" update=":form:display"
oncomplete="dlg.show()" listener="#{user.selected()}"/>
<p:column headerText="User-ID" filterBy="#{row.userID}">
<h:outputText value="#{row.userID}" />
</p:column>
<p:column headerText="Name" filterBy="#{row.userName}">
<h:outputText value="#{row.userName}" />
</p:column>
<p:column headerText="Threat" filterBy="#{row.attackID}">
<h:outputText value="#{row.attackID}" />
</p:column>
<p:column headerText="Rank">
<h:outputText value="#{row.rank}" />
</p:column>
</p:dataTable>
<p:dialog id="tDialog" header="Threat info" widgetVar="dlg"
modal="true" height="250" width="300" showEffect="explode"
hideEffect="explode">
<h:panelGrid id="display" columns="2" cellpadding="4">
<h:outputText value="Attack ID:" />
<h:outputText value="#{user.selectedUser.attackID} " />
<h:outputText value="Name:" />
<h:outputText value="#{user.selectedUser.attackName}" />
<h:outputText value="Action Taken:" />
<h:outputText value="#{user.selectedUser.actionTaken}" />
<h:outputText value="Attack Time:" />
<h:outputText value="#{user.selectedUser.attackTime }" />
</h:panelGrid>
</p:dialog>
</h:form>
</h:body>