When ircd started supporting link compression the current zlib version was 1.0.4 and I expect that most people are probably still using this version. Even tho 1.0.4 has been used for a long time with little or no problem, I now have evidence that this version contains serious bugs, so I would like to recommend upgrading to a more recent version. http://www.cdrom.com/pub/infozip/zlib/