Intermittent exceptions during startup

[Jon Keys]

I sometimes see this stacktrace when starting my app (I'm using the current master):

java.lang.LinkageError: loader (instance of  org/vertx/java/platform/impl/ModuleClassLoader): attempted  duplicate class definition for name: "org/vertx/groovy/core/AsyncResult"

    at java.lang.ClassLoader.defineClass1(Native Method)

    at java.lang.ClassLoader.defineClass(ClassLoader.java:800)

    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)

    at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)

    at java.net.URLClassLoader.access$100(URLClassLoader.java:71)

    at java.net.URLClassLoader$1.run(URLClassLoader.java:361)

    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)

    at java.security.AccessController.doPrivileged(Native Method)

    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)

    at org.vertx.java.platform.impl.ModuleClassLoader.doLoadClass(ModuleClassLoader.java:90)

    at org.vertx.java.platform.impl.ModuleClassLoader.loadClass(ModuleClassLoader.java:70)

    at java.lang.ClassLoader.loadClass(ClassLoader.java:412)

    at groovy.lang.GroovyClassLoader.loadClass(GroovyClassLoader.java:648)

    at groovy.lang.GroovyClassLoader.loadClass(GroovyClassLoader.java:516)

    at org.codehaus.groovy.control.ClassNodeResolver.tryAsLoaderClassOrScript(ClassNodeResolver.java:183)

    at org.codehaus.groovy.control.ClassNodeResolver.findClassNode(ClassNodeResolver.java:168)

    at org.codehaus.groovy.control.ClassNodeResolver.resolveName(ClassNodeResolver.java:124)

    at org.codehaus.groovy.control.ResolveVisitor.resolveToOuter(ResolveVisitor.java:616)

    at org.codehaus.groovy.control.ResolveVisitor.resolve(ResolveVisitor.java:268)

    at org.codehaus.groovy.control.ResolveVisitor.visitClass(ResolveVisitor.java:1140)

    at org.codehaus.groovy.control.ResolveVisitor.startResolving(ResolveVisitor.java:141)

    at org.codehaus.groovy.control.CompilationUnit$10.call(CompilationUnit.java:632)

    at org.codehaus.groovy.control.CompilationUnit.applyToSourceUnits(CompilationUnit.java:912)

    at org.codehaus.groovy.control.CompilationUnit.doPhaseOperation(CompilationUnit.java:574)

    at org.codehaus.groovy.control.CompilationUnit.compile(CompilationUnit.java:523)

    at groovy.lang.GroovyClassLoader.doParseClass(GroovyClassLoader.java:279)

    at groovy.lang.GroovyClassLoader.parseClass(GroovyClassLoader.java:258)

    at groovy.lang.GroovyClassLoader.parseClass(GroovyClassLoader.java:244)

    at org.vertx.groovy.platform.impl.GroovyVerticleFactory.createVerticle(GroovyVerticleFactory.groovy:71)

    at org.vertx.java.platform.impl.DefaultPlatformManager$19.run(DefaultPlatformManager.java:1541)

    at org.vertx.java.core.impl.DefaultContext$3.run(DefaultContext.java:176)

    at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:354)

    at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:353)

    at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:101)

    at java.lang.Thread.run(Thread.java:744)

I'm unable to find a way to reliably reproduce the error.
Usually I can just kill the process and restart it without issue.

Any ideas what might be causing this?