java project won't compile class referencing enum depending on source code order

Question

I have an situation where some Java 1.6 sources won't compile in Maven and only compile in javac when I specify sources in a certain order.

pom.xml is bare-bones but specifies -source and -target of 1.6:

 <build>
     <plugins>
         <plugin>
             <groupId>org.apache.maven.plugins</groupId>
             <artifactId>maven-compiler-plugin</artifactId>
             <version>3.1</version>
             <configuration>
                 <source>1.6</source>
                 <target>1.6</target>
             </configuration>
         </plugin>
     </plugins>
 </build>

ComputeOperation.java

package test.domain;

public interface ComputeOperation<T> {

    public T compute(T arg1, T arg2);
}

Computations.java

 package test.domain;

 public enum Computations implements ComputeOperation<Integer> {

     ADD {
         @Override
         public Integer compute(Integer arg1, Integer arg2) {
             return arg1 + arg2;
         }
     },

     SUBTRACT {
         @Override
         public Integer compute(Integer arg1, Integer arg2) {
             return arg1 - arg2;
         }
     }

 } 

App.java

package test.app;    

import test.domain.*;    

public class App {
    public static void main( String[] args ) {
        System.out.println(Computations.ADD.compute(1, 1));
    }
}

Maven build fails as follows (full debug log here):

[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] /home/nzucker/projects/maven-test/src/main/java/test/app/App.java:[7,44] cannot find symbol
symbol : method compute(int,int)
location: class test.domain.Computations
[INFO] 1 error

Plain old javac compilation fails succeeds if App.java comes before Computations.java:

[nzucker:maven-test]$ javac -source 1.6 -target 1.6 -g -d target/classes src/main/java/test/app/App.java src/main/java/test/domain/Computations.java src/main/java/test/domain/ComputeOperation.java
src/main/java/test/app/App.java:7: cannot find symbol
symbol  : method compute(int,int)
location: class test.domain.Computations
    System.out.println(Computations.ADD.compute(1, 1));
                                       ^
1 error

But the build succeeds if I put App.java last in the input sources:

[nzucker:maven-test]$ javac -source 1.6 -target 1.6 -g -d target/classes  src/main/java/test/domain/Computations.java src/main/java/test/domain/ComputeOperation.java src/main/java/test/app/App.java 
[nzucker:maven-test]$ java -cp target/classes/ test.app.App
2

Finally, if I change the import in App.java to a static import, compilation succeeds:

package test.app;

import static test.domain.Computations.*;

public class App {
    public static void main( String[] args ) {
        System.out.println(ADD.compute(1, 1));
    }
}

Questions:

I am aware of "Workaround for javac compilation order bug in maven" - so my question is why is this occurring? Is this a true defect in Maven? If so, what is the JIRA issue if so?

Also, why does compilation fail? I thought that javac resolve dependencies and compilation order between classes during a pre-processing phase? I guess I was wrong? Is there a specification that covers this?

Ok, the other question I linked to has a response that points to a bug in Java 1.6. The answer is to upgrade to Java 1.7 or implement a work-around.