FULL PRODUCT VERSION :
java version "1.8.0_25"
Java(TM) SE Runtime Environment (build 1.8.0_25-b18)
Java HotSpot(TM) 64-Bit Server VM (build 25.25-b02, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Windows 8 64 bit

A DESCRIPTION OF THE PROBLEM :
Maven compilation with annotation processing enabled fails, if the target/generated-sources/metamodel directory is not empty.
If it's not empty, javac fails to compile.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Create at least 1 JPA entity (@Entity) and a persistence unit
Configure maven to use an annotation processor (QueryDSL 3.6 or eclipseLink 2.5.2)  during compilation (both tested, giving the same exception)
run: mvn compile twice, without using mvn clean in between, i.e.
> mvn clean compile
> mvn compile


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
compilation succeeds both times
ACTUAL -
The first compilation succeeds. the second fails with an exception.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
[INFO] Compiling 108 source files to myproject\target\classes
An exception has occurred in the compiler (1.8.0_25). Please file a bug at the Java Developer Connection (http://java.sun.com/webapps/bugreport)  after checking the Bug Parade for
duplicates. Include your program and the following diagnostic in your report.  Thank you.
java.lang.IllegalStateException: endPosTable already set
        at com.sun.tools.javac.util.DiagnosticSource.setEndPosTable(DiagnosticSource.java:136)
        at com.sun.tools.javac.util.Log.setEndPosTable(Log.java:350)
        at com.sun.tools.javac.main.JavaCompiler.parse(JavaCompiler.java:667)
        at com.sun.tools.javac.main.JavaCompiler.parseFiles(JavaCompiler.java:950)
        at com.sun.tools.javac.processing.JavacProcessingEnvironment$Round.<init>(JavacProcessingEnvironment.java:892)
        at com.sun.tools.javac.processing.JavacProcessingEnvironment$Round.next(JavacProcessingEnvironment.java:921)
        at com.sun.tools.javac.processing.JavacProcessingEnvironment.doProcessing(JavacProcessingEnvironment.java:1187)
        at com.sun.tools.javac.main.JavaCompiler.processAnnotations(JavaCompiler.java:1170)
        at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:856)
        at com.sun.tools.javac.main.Main.compile(Main.java:523)
        at com.sun.tools.javac.api.JavacTaskImpl.doCall(JavacTaskImpl.java:129)
        at com.sun.tools.javac.api.JavacTaskImpl.call(JavacTaskImpl.java:138)
        at org.codehaus.plexus.compiler.javac.JavaxToolsCompiler.compileInProcess(JavaxToolsCompiler.java:125)
        at org.codehaus.plexus.compiler.javac.JavacCompiler.performCompile(JavacCompiler.java:169)
        at org.apache.maven.plugin.compiler.AbstractCompilerMojo.execute(AbstractCompilerMojo.java:823)
        at org.apache.maven.plugin.compiler.CompilerMojo.execute(CompilerMojo.java:129)
        at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:132)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:208)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
        at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:116)
        at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:80)
        at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:51)
        at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:120)
        at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:347)
        at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:154)
        at org.apache.maven.cli.MavenCli.execute(MavenCli.java:582)
        at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:214)
        at org.apache.maven.cli.MavenCli.main(MavenCli.java:158)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:483)
        at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
        at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
        at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
        at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
SampleEntity.java:

@Entity
public class SampleEntity {
	@Id
	public long id;
	
	@Version
	public long version;
	
	public String name;
	
}

maven POM:
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.test</groupId>
    <artifactId>mavenproject1</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging>
    
    <properties>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
        <failOnMissingWebXml>false</failOnMissingWebXml>
    </properties>
	
	<build>
		<plugins>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-compiler-plugin</artifactId>
				<version>3.2</version>
				<configuration>
					<encoding>${project.build.sourceEncoding}</encoding>
					<generatedSourcesDirectory>${basedir}/target/generated-sources/metamodel</generatedSourcesDirectory>
					<showWarnings>true</showWarnings>
					<optimize>true</optimize>
					<showDeprecation>true</showDeprecation>
					<compilerId>javac</compilerId>
					<!-- <verbose /> -->
					<annotationProcessors>
						<annotationProcessor>com.mysema.query.apt.jpa.JPAAnnotationProcessor</annotationProcessor>
					</annotationProcessors>
				</configuration>
			</plugin>
		</plugins>
	</build>
	<dependencies>
		<dependency>
            <groupId>javax</groupId>
            <artifactId>javaee-api</artifactId>
            <version>7.0</version>
            <scope>provided</scope>
        </dependency>
		<!-- Needed for annotation processing only -->
		<dependency>
			<groupId>com.mysema.querydsl</groupId>
			<artifactId>querydsl-apt</artifactId>
			<version>3.6.0</version>
			<classifier>jpa</classifier>
			<scope>provided</scope>
		</dependency>
    </dependencies>
</project>
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
none known