I am new user of jqgrid, i tried to use multi grouping

here is sample page  http: // configuratorlct.walshdemo.com/Content/jqGrid/GlobalItemTypeDemoPage.html

problem is , I grouped the list by item type and item column, when I first load the list , it seems the grouped list is incorrect, you can see the Floor has 7 sub items(4 of them are duplicated) which should be 3 ,

can anyone help me?

thanks advance