It would be interesting to see if any popular ZIP libraries have a similar issue. If you add a file that's already in the archive, for example, and the new one

It would be interesting to see if any popular ZIP libraries have a similar issue. If you add a file that's already in the archive, for example, and the new one is larger, I could see it just sticking the new one at the end of the archive and appending a new central directory structure. Is the periodic reencoding of the huffman tree part of DEFLATE or in the PNG are they just using a sequence of separate DEFLATE structures appended together that each have their own huffman tree? If it's the former, you might be able to recover part of a ZIP archive entry that was reduced in size and written over the original version.