compilation mismatch between javac 8 source 7 and javac 7 source 7

The following code:

import java.util.Comparator;

class GenericMethod {
     <E extends Comparable<E>> Comparator<E> getComparator() {
         return null;
     }

     <E> void useComparator(Comparator<? super E> comparator) {
     }

     void test() {
         useComparator(this.getComparator());
     }
}

Compiles with javac8 -target 7 but fails to compile with javac7 target 7.