This is easy to fix.
When creating a ZIP with plexus-archiver, normally directories are added with a wrong attribute.
Listing such a ZIP file with "zipinfo" or "unzip -Z" in the command line shows directories as having the attribute "?" instead of "d". Such files cannot be opened with Midnight Commander or Krusader.
This behavior is there since plexus-archiver 1.0-alpha-12; version 1.0-alpha-10 didn't have it.
I've attached a patch which I have tested with the actual trunk version 1.3-SNAPSHOT and it works. Also the unit tests finish successfully.
This can be tested with maven-assembly-plugin:2.2-beta-5 for example, which depends on plexus-archiver 1.0-alpha-12.
maven-assembly-plugin:2.2-beta-2 in turn uses plexus-archiver 1.0-alpha-10 and doesn't show this behaviour.
I would have commited the fix into SVN myself if I had an account...