Split and simplify the following sentence while retaining its full meaning: Whereas , in the case of mixtures of cereals , rice and broken rice , the tariff classification may give rise to difficulties if determined in accordance with these rules ; whereas in fact such classification sometimes results in a low import levy being charged on mixtures which , however , contain a substantial proportion of products subject to a high import levy.
 Simplified version:
In the case of mixtures of grain , rice and broken rice , the tariff classification according to these regulations can lead to difficulties . This tariff classification means that in certain cases a small levy is applied to individual mixtures even though they contain a substantial percentage of products to which a high levy applies .