Strange behaviour of image uploader

CKEDITOR.replace( '<%=txtEditor.ClientID %>',
{
    filebrowserImageBrowseUrl : 'Browser.aspx?type=Images',
    filebrowserFlashBrowseUrl :'Browser.aspx?type=Flash',
    filebrowserImageUploadUrl : 'Uploader.aspx?type=Images',
    filebrowserFlashUploadUrl : 'Uploader.aspx?type=Flash',
    filebrowserWindowWidth : '600',
    filebrowserWindowHeight : '400'
});