It looks like the map contains entries in the mpq hash table that were put there with the intention of making it crash if a program attempted to read it without checking the validity of a certain value.  Apparently the file listing function in my mpq library was not made to handle such invalid entries.

I've updated the function in my mpq library source code to deal with the invalid data.  The WinMPQ download has been updated with a new build of the library from that version of the code.

Personally, I prefer to have bugs fixed, rather than leaving them there just so that "map protectors" can exploit them.