http://mail.openjdk.java.net/pipermail/jmh-dev/2014-August/001329.html

Providing a base class with:

class SuperClass {
    @Benchmark
    public void myBenchmark() { ... }
}

...and the subclass with the same:

class SubClass extends SuperClass {
    @Benchmark
    public void myBenchmark() { ... }
}

Yields the cryptic message:
    Internal error: multiple methods per @Group, but not all methods have @Group

(or, in recent JMH versions, "Duplicate @Benchmark method. JMH needs an uniquely named method, regardless of the arguments list.")

This is because the @Benchmark lookup code treats both methods are distinct methods, and tries to put them in the same group.