jQuery Grid Plugin - jqGrid

I have a grid using inline edit that allows adding multiple blank rows, but this is causing some problems.

If I add two or more rows and leave some of them with errors, the other rows (saverow succeeded) turn all columns to read-only, with the exception of a select column (edittype: select) with custom formatter to return the combo box text instead of value.

Here is a sample of my code:

<script type="text/javascript">
jQuery(document).ready(function () {
jQuery('#grid').jqGrid({
autowidth:true,
datatype:'local',
height:'100%',
pager:'#pager',
rowNum:10,
sortname:'User',
viewrecords:true,
gridComplete: function() {OnGridComplete()},
onSelectRow: function(rowid, status) {OnSelectRow(rowid, status)},
colModel: [
{
name:'AlternativeIndex',
hidden:true,
key:true,
index:'AlternativeIndex'
},{
name:'UserId',
formatter: formatUserAsDropDown,
label:'User',
sortable:true,
width:300,
editable:true,
edittype:'select',
editoptions:{"value":""},
index:'UserId'
},{
name:'Permission',
formatter:'select',
hidden:false,
label:'Permission',
sortable:true,
width:170,
editable:true,
edittype:'select',
editoptions:{"value":"R:Read;W:Write"},
index:'Permission'
}
]
});
});
</script>

And here is the code for the custom formatter:

function formatUserAsDropDown(cellvalue, options, rowObject) {
    return rowObject.Username;
}

This problem does not occur with Permission column.

PS: I cannot reload the grid after saverow as there maybe have some rows with errors and I have to keep them editable until the user fix these errors and click on Save button again.