FULL PRODUCT VERSION :
java version "1.8.0_112"
Java(TM) SE Runtime Environment (build 1.8.0_112-b15)
Java HotSpot(TM) 64-Bit Server VM (build 25.112-b15, mixed mode)

java version "9-ea"
Java(TM) SE Runtime Environment (build 9-ea+144)
Java HotSpot(TM) 64-Bit Server VM (build 9-ea+144, mixed mode)

A DESCRIPTION OF THE PROBLEM :
I'm a developer of the JaCoCo code coverage library.
While preparing test cases for instrumentation of annotations, I encountered this issue and isolated a simple reproducer.


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile and start the source code below.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
No exception
ACTUAL -
java.lang.annotation.AnnotationFormatError: Malformed method on an annotation type
        at sun.reflect.annotation.AnnotationInvocationHandler.validateAnnotationMethods(AnnotationInvocationHandler.java:384)

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.reflect.Method;

class AnnotationBug {
  @Retention(RetentionPolicy.RUNTIME)
  @interface Annotation {
    // provoke creation of method
    Runnable r = () -> {};
  }

  @Annotation
  public static void m1() {
  }

  @Annotation
  public static void m2() {
  }

  @Annotation
  public static void main(String[] args) throws Exception {
    Annotation a1 = AnnotationBug.class.getMethod("m1").getAnnotation(Annotation.class);
    Annotation a2 = AnnotationBug.class.getMethod("m2").getAnnotation(Annotation.class);
    // provoke verification in AnnotationInvocationHandler
    a1.equals(a2);
  }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Don't test wired corner cases ;-)