Checkbox and Datatable problem in JSF

When I am using a t:selectBooleanCheckbox inside a t:datatable the checkbox doesn't retain the selections that the user made in the first request. In the subsequent requests the selections are retained. This seems to be a very common problem when I searched google. But unfortunately I could not find any solution for solving this.

<t:dataTable border="1" value="#{bb_ValuationDashboard.snapshotRoundDTO.fmisPurSalesDtls}"
	var="purchasedSales" 
	styleClass="dataTable" width="100%">
	<t:column width="3%">
		<f:facet name="header">
			<t:outputText styleClass="styTblHeaderNew" value="Select Checkbox to select row"></t:outputText>
		</f:facet>
		<t:selectBooleanCheckbox forceId="true" id="purSles" value="#{purchasedSales.isSelected}" />
	</t:column>
	<t:column width="14%">
		<f:facet name="header">
			<t:outputText styleClass="styTblHeaderNew" value="#{valDash.ss_displayPanel_purSalesTab_Address}"></t:outputText>
		</f:facet>
		<t:outputText value="#{purchasedSales.propertyAddress.addressLine1} 
		#{purchasedSales.propertyAddress.addressLine2} 
		#{purchasedSales.propertyAddress.city}  
		#{purchasedSales.propertyAddress.stateCode} " id="pAddress"></t:outputText>
	</t:column>							
</t:datatable>