var prm = Sys.WebForms.PageRequestManager.getInstance();
prm.add_endRequest(EndRequest);

function EndRequest(sender, args) {
    switch (sender._postBackSettings.sourceElement.id) {
        case $('input[id$=\'btnInsert\']').attr('id'):
            Miscellaneous.setEditorValue($('input[id$=\'txtComment\']').attr('id'), '');
            focus($get('postComment'));
            break;
    }
}