Column herder width set to 0 when using with vertical scroll

Mandeepsg3

http://debug.datatables.net/evaviz

above it the debugger output.

by enabling vertical scroll by adding option
"sScrollY": "450px",
"paging": false ,

the column header width is set to 0

here is how i have initialized table

var oTableSubjectsDetails = $('#subjectsDetails').DataTable({
bJQueryUI: true,
"aaSorting": [[ 0, "asc" ]],
"sScrollY": "450px",
"paging": false ,
"bProcessing": true,
"bFilter": false,
"bAutoWidth": false,
"oLanguage":
{
"sZeroRecords": "No records.",
},
"aoColumns": [
{ "sWidth": "10%" },
{ "sWidth": "20%" },
{ "sWidth": "20%" },
{ "sWidth": "15%" },
{ "sWidth": "15%" },
{ "sWidth": "20%" }

        ]         
});   

Any idea how to get the width of the header correctly calculated.