Failed to access file due to locked access when using more than one Maven worker thread

My multi-module POM contains of ten modules. Each of those modules does the same: Invoke the 'copy' goal of the dependency plugin. The idea is to have ten copies of the identical source, which then end up in ten different targets by getting furthere processed.

As long as I do not use more than one Maven worker thread, everything works well always. But when using -T 5 to have five worker threads, rather often the reactor fails because the source file is locked:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-dependency-plugin:2.8:copy (copy) on project MYARTIFACT: Unable to resolve artifact. Could not transfer artifact mygroup:myartifact:dll:4.36.1-20140415.143537-37 from/to nexus (http://nexus/nexus/content/groups/public): C:\Users\jenkins.QUIPSY\.m2\repository\mygroup\myartifact\4.36.1-SNAPSHOT\myartifact-4.36.1-20140415.143537-37.dll (The process cannot access the file, because it is in use by another process)

So it seems that the 'copy' task actually is locking the source file, which is not multi-threading-compatible. Hence, either that is a bug and should get fixed, or it is on purpose, then this goal has to be marked as non-multithreading-able.