The reason for the two classification is because of the ingress protection against water jet sprays for wich it is just classified IP65 (it is not protected against heavy water jet sray for at least 3 minutes), but it is classified IP68 in concern to water immersion (it is protected against the effects of continued immersion in water at depths greater than 1 metre). Please remember that this classifications are obtained under laboratory conditions.
For more clear information please read here.
