Synchronization issue with parallel downloads

> [java] java.util.ConcurrentModificationException
> [java] at java.util.LinkedList$ListItr.checkForComodification(LinkedList.java:552)
> [java] at java.util.LinkedList$ListItr.next(LinkedList.java:488)
> [java] at org.codehaus.plexus.component.configurator.converters.lookup.DefaultConverterLookup.findConverterForType(DefaultConverterLookup.java:113)
> [java] at org.codehaus.plexus.component.configurator.converters.lookup.DefaultConverterLookup.lookupConverterForType(DefaultConverterLookup.java:92)
> [java] at org.codehaus.plexus.component.configurator.converters.ComponentValueSetter.initSetter(ComponentValueSetter.java:92)
> [java] at org.codehaus.plexus.component.configurator.converters.ComponentValueSetter.<init>(ComponentValueSetter.java:62)
> [java] at org.codehaus.plexus.component.configurator.converters.composite.ObjectWithFieldsConverter.processConfiguration(ObjectWithFieldsConverter.java:134)
> [java] at org.codehaus.plexus.component.configurator.BasicComponentConfigurator.configureComponent(BasicComponentConfigurator.java:56)
> [java] at org.codehaus.plexus.component.configurator.AbstractComponentConfigurator.configureComponent(AbstractComponentConfigurator.java:54)
> [java] at org.codehaus.plexus.component.configurator.AbstractComponentConfigurator.configureComponent(AbstractComponentConfigurator.java:47)
> [java] at org.apache.maven.artifact.manager.DefaultWagonManager.configureWagon(DefaultWagonManager.java:1058)
> [java] at org.apache.maven.artifact.manager.DefaultWagonManager.configureWagon(DefaultWagonManager.java:1038)
> [java] at org.apache.maven.artifact.manager.DefaultWagonManager.getRemoteFile(DefaultWagonManager.java:418)
> [java] at org.apache.maven.artifact.manager.DefaultWagonManager.getArtifact(DefaultWagonManager.java:372)
> [java] at org.apache.maven.artifact.manager.DefaultWagonManager.getArtifact(DefaultWagonManager.java:327)
> [java] at org.apache.maven.artifact.resolver.DefaultArtifactResolver.resolve(DefaultArtifactResolver.java:216)
> [java] at org.apache.maven.artifact.resolver.DefaultArtifactResolver.resolve(DefaultArtifactResolver.java:90)
> [java] at org.apache.maven.artifact.resolver.DefaultArtifactResolver$ResolveArtifactTask.resolveArtifact(DefaultArtifactResolver.java:453)
> [java] at org.apache.maven.artifact.resolver.DefaultArtifactResolver$ResolveArtifactTask.run(DefaultArtifactResolver.java:434)
> [java] at edu.emory.mathcs.backport.java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1061)
> [java] at edu.emory.mathcs.backport.java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:575)
> [java] at java.lang.Thread.run(Thread.java:534)
>