This is an old thread, but I seem to have resolved the Fedora 14+ (and maybe other distributions) issue.  For anyone who wants the gory details, basically libxml2 makes some assumptions about the implementation of zlib based on the version of zlib reported in zlib.h; these assumptions are invalid for zlib version 1.2.4 and newer.  Though I build for LSB (Linux Standards Base) 3.1, which includes zlib 1.2.1, the libraries used at runtime might actually be a different version, and LSB is apparently OK with that because the API (or at least the restricted API exported by LSB 3.1) doesn't change.between versions.  Needless to say, libxml2 makes some assumptions that are outside the LSB specification.  I have resolved this by making sure libxml2 compiles and links to a static libz.a (version 1.2.5), and won't ever use a dynamic version.  (Other parts of the system, like dcmtk, will still use whatever libz is available).

Long story short, releases tagged with "lsb31" starting with 1.9.9.5 are expected to work on all LSB 3.1 and newer distributions, even those (like Fedora 14/15/...) that ship with a version of zlib >= 1.2.4.