composer: Wrong directory structure after unpacking if zip contains only a directory

Hi,

we have the following structure in some of our Zips:

package/
    src/
        PhpFile1.php
        PhpFile2.php

However, after installing this package the directory structure suddenly differes from the one in the archive:

src/
    PhpFile1.php
    PhpFile2.php

We identified the code which causes this (wrong) behavior at ArchiveDownloader.php.

Is there any reason for this behavior? I think it clearly is a bug.