Silly question - why does bundled vs. external zlib influence the commandline parameters at all? I don't see why a user would have to use a different commandline parameter just because an internal detail of rsync changed. According to this https://bugzilla.samba.org/show_bug.cgi?id=10372#c14 there is some problem with the system libz, so the new compression scheme was created to work with system libz. Unfortunately it is incompatible to the previous compression. There seem to be some modifications necessary to libz to support
http://bugzilla.opensuse.org/show_bug.cgi?id=1046197
http://bugzilla.opensuse.org/show_bug.cgi?id=1046197#c5
--- Comment #5 from Ralf Friedl