jQuery Grid Plugin - jqGrid

I tried creating following field in my grid

{name:'taxtype',index:'taxtype',width:5,search:false,edittype:'select',editable:true,hidden:true,editrules: {edithidden:true, required:true}, editoptions: {readonly:'readonly', value: "T:Taxable;NT:Non Taxable;B:Both" }

This creates following HTML output

<select role="select" id="taxtype" name="taxtype" size="1" class="FormElement" readonly="readonly"><option role="option" value="T">Taxable</option><option role="option" value="NT">Non Taxable</option><option role="option" value="B">Both</option></select>

----------------The Issue-----------------

I am still able to select values from the list both in and/edit mode, this field is suppose to be non-editable/selectable as its true with other edittypes.