i am creating a visualforce page . i am using dynamic component in it. my visual force page code is

<apex:page title="Opportunity Display" controller="MyPageController1" showHeader="true" sidebar="false" readOnly="true" cache="false">
<apex:sectionHeader subtitle="SOQL Offset Example w/Dynamic Page Buttons" title="Opportunity Display Table"/>
<apex:form >
<apex:pageBlock >   
<apex:dynamicComponent componentValue="{!myCommandButtons}"/>   
    <apex:actionFunction action="{!refreshGrid}"  name="queryByPage" reRender="myPanel,myButtons" >
        <apex:param name="firstParam" assignTo="{!selectedPage}" value="" />
    </apex:actionFunction>



 <apex:pageBlockSection title="Opportunity Display (Total List Size: {!total_size})" collapsible="false">
    <apex:outputPanel id="myPanel">
    <apex:pageMessages id="theMessages" />
    <apex:pageBlockTable value="{!opportunity}" var="n" align="center">
   <apex:column ><apex:inputCheckbox value="{!n.checked}"/></apex:column>
        <apex:column value="{!n.cat.Id}" />
        <apex:column value="{!n.cat.Name}" />
        <apex:facet name="footer">Showing Page # {!pageNumber} of {!totalPages}</apex:facet>
    </apex:pageBlockTable>
    </apex:outputPanel>
    </apex:pageBlockSection>  


</apex:pageBlock>  

</apex:form>
</apex:page>

and the code segment from where i am retrieving dynamic component is

public Component.Apex.pageBlockButtons getMyCommandButtons() {

        //the reRender attribute is a set NOT a string
        Set<string> theSet = new Set<string>();
        theSet.add('myPanel');
        theSet.add('myButtons');

        integer totalPages;
        if (math.mod(total_size, list_size) > 0) {
            totalPages = total_size/list_size + 1;
        } else {
            totalPages = (total_size/list_size);
        }

        integer currentPage;        
        if (selectedPage == '0') {
            currentPage = counter/list_size + 1;
        } else {
            currentPage = integer.valueOf(selectedPage);
        }

        Component.Apex.pageBlockButtons pbButtons = new Component.Apex.pageBlockButtons();        
    pbButtons.location = 'both' ;
        pbButtons.id = 'myPBButtons';

        Component.Apex.outputPanel opPanel = new Component.Apex.outputPanel();
        opPanel.id = 'myButtons';

        //the Previous button will alway be displayed
        Component.Apex.commandButton b1 = new Component.Apex.commandButton();
        b1.expressions.action = '{!Previous}';
        b1.title = 'Previous';
        b1.value = 'Previous';
        b1.expressions.disabled = '{!disablePrevious}';        
        b1.reRender = theSet;

        opPanel.childComponents.add(b1);        

        for (integer i=0;i<totalPages;i++) {
            Component.Apex.commandButton btn = new Component.Apex.commandButton();

            if (i+1==1) {
                btn.title = 'First Page';
                btn.value = 'First Page';
                btn.rendered = true;                                        
            } else if (i+1==totalPages) {
                btn.title = 'Last Page';
                btn.value = 'Last Page';
                btn.rendered = true;                            
            } else {
                btn.title = 'Page ' + string.valueOf(i+1) + ' ';
                btn.value = ' ' + string.valueOf(i+1) + ' ';
                btn.rendered = false;             
            }

            if (   (i+1 <= 5 && currentPage < 5)
                || (i+1 >= totalPages-4 && currentPage > totalPages-4)
                || (i+1 >= currentPage-2 && i+1 <= currentPage+2))
            {
                btn.rendered = true;
            }

            if (i+1==currentPage) {
                btn.disabled = true; 
                btn.style = 'color:blue;';
            }  

            btn.onclick = 'queryByPage(\''+string.valueOf(i+1)+'\');return false;';

            opPanel.childComponents.add(btn);

            if (i+1 == 1 || i+1 == totalPages-1) { //put text after page 1 and before last page
                Component.Apex.outputText text = new Component.Apex.outputText();
                text.value = '...';        
                opPanel.childComponents.add(text);
            } 

        }

        //the Next button will alway be displayed
        Component.Apex.commandButton b2 = new Component.Apex.commandButton();
        b2.expressions.action = '{!Next}';
        b2.title = 'Next';
        b2.value = 'Next';
        b2.expressions.disabled = '{!disableNext}';        
        b2.reRender = theSet;
        opPanel.childComponents.add(b2);

        //add all buttons as children of the outputPanel                
        pbButtons.childComponents.add(opPanel);  

        return pbButtons;

    }    
    at this line i am setting 
 pbButtons.location = 'both' ;

so it will render bottom and top but button is rendering only at top not at bottom and when i set this line to pbButtons.location='bottom' then there is no pageblock button in the page .can any one please tell why its not rendering at the bottom??