The most prevalent type of Kashrus mislabeling is the inadvertently dropped Dairy designation.  It is recommended that you check unfamiliar products that have a Kosher Symbol without any Dairy or Parve designation for milk, whey, butter, casein, lactose, and lactic acid (which may be either dairy or parve).  In cases of uncertainty you should feel free to call the agency that certifies the product.  The major agencies are happy to answer any questions that the consumers might have.