The copy of zlib embedded in librpmio.so does not have symbol names changed to avoid clashes with libz.so. Potential mess if an application dlopens librpmio and the system libz.so has a different ABI to the copy of zlib embedded in librpmio. I'll attach the list of symbols.
Created attachment 98183 [details] list of symbols duplicated between libz and librpmio
Yup, pissed away 5 days figgering the symbol pollution w yum 2 weeks ago. rpm-4.3 is built now (and has been for the last 2 weeks) without internal zlib.