Today when you run a "hadoop jar" command, the jar is unzipped to a temporary location and gets added to the classloader.
However, the original jar itself is still added to the classpath.
As a result, the contents of the jar are present in the classpath twice and are completely redundant. Although this does not necessarily cause correctness issues, some stricter code written to require a single presence of files may fail.
I cannot think of a good reason why the jar should be added to the classpath if the unjarred content was added to it. I think we should remove the jar from the classpath.