I think this started with B11 - when you download a post with a single zip file it will unzip that file. So far so good. What's not so good is that when doing the unzip it completely mashes up the directory hierarchy. Instead of unzipping to the hierarchy contained in the zip file, it flattens the directory structure, and prepends the directory path information to the leaf file names.
Not sure if this has been reported before. Lots of examples can be found in alt.binaries.mac.applications.
Thanks!