Product Approval

Here, im using a wrapper class to display the list of products from the opportunity and using a checkbox when the user selects the products and clicks "approve" button i update a field with the value "Approved"  in the product record.

The problem im facing here is, when i select all the products and click "approve" the update works. And for the first time if i select one product of the two products and click "approve", the update works. But the next time if i select the other product and click "approve" the button is not getting fired. While the second time i click the same "approve" consecutively it works. Im not able to figure out whats the reason for this behaviour.

Please suggest what to do.

Code:

public class cls_Approve
{
    public cls_Approve(ApexPages.StandardController controller)
    {
        opp = (opportunity)controller.getRecord();        
        oppLineItem = [Select PricebookEntry.Product2.id,PricebookEntry.Product2.name , PricebookEntry.Product2.HD_Product_Approval__c from OpportunityLineItem where OpportunityId  =: opp.id];
    }
    public class wrapProduct
    {
        public boolean chkProduct{get;set;}       
        public string wrapLineItemName{get;set;}
        public string wrapLineItemId{get;set;}
        public Opportunity wrapOpp{get;set;}      
        public wrapProduct(Opportunity op)
        {
            wrapOpp =  op;
        }
    }       
    public List<wrapProduct> getwrapProdList()
    {
        queryResults = new List<wrapProduct>();
        for(opportunityLineItem oli : oppLineItem)
        {
            wrapProduct wpObj = new wrapProduct(opp);          
            if(oli.PricebookEntry.Product2.name != null)
            {                
                wpObj.wrapLineItemName = oli.PricebookEntry.Product2.name;
            }
            wpObj.wrapLineItemId = oli.PricebookEntry.Product2.id;                            
            queryResults.add(wpObj);
        }        
        return queryResults;            
    }                 
    public List<string> updateProdId = new List<string>();
    public List<product2> updateProd2 = new List<product2>();
    public List<product2> pList = new List<product2>();   
    public pagereference approveProduct()
    {                                         
        for(wrapProduct wpList:queryResults)
        {                                         
            if(wpList.chkProduct == true)
            {
                updateProdId.add(wpList.wrapLineItemId);                         
            }                       
        }        
        if(updateProdId.size() >0)
        {                        
            pList = [select HD_Product_Approval__c from  product2 where id in: updateProdId];           
        }
        for(product2 p2:pList)
        {            
            p2.HD_Product_Approval__c = 'Approved';
            updateProd2.add(p2);                                       
        }       
        update updateProd2;          
        return null;
    }        
}

VisualForce Page:

--------------------------

<apex:page id="Page1" standardController="opportunity" extensions="cls_Approve">
    <apex:form id="form1">        
        <b>Product Approval</b>
        <apex:repeat value="{!wrapProdList}" var="oli">             
            <table border='1'>
                <tr>
                    <td align="center">
                        <apex:inputCheckbox id="chkProd" value="{!oli.chkProduct}" disabled="{!oli.disableChkProduct}"/>     
                    </td>
                    <td align="center">
                        <b> Product : </b>     
                    </td>
                    <td>
                        <apex:outputText value="{!oli.wrapLineItemName}"/>
                    </td>                        
                </tr>              
            </table>
        </apex:repeat>
        <apex:commandButton value="approve" action="{!approveProduct}" rerender="table1" disabled="{!fnProdApprove}"/>      
    </apex:form>   
</apex:page>