Проблема с переносом заголовков столбцов jqGrid в IE

I'm using jqGrid in my pages, I modified the ui.jqgrid.css file to wrap the column headers like this:

.ui-jqgrid tr.jqgrow td {
    white-space: normal !important;
}

.ui-th-column,.ui-jqgrid .ui-jqgrid-htable th.ui-th-column{
    white-space:normal;
}

It works fine in all of the browsers but IE! I tried IE7 and IE8 and the problem is still out there.