Technically, this might be invalid, it's still a regression to 1.2.3-r1, though. When I was building a package, that uses cmake, that built fine with 1.2.3-r1, I was surprised by an error: No rules to make `/lib/libz.so', needed by '...' 1.2.3-r1 was doing dosym libz.so.${PV} /$(get_libdir)/libz.so dosym libz.so.${PV} /$(get_libdir)/libz.so.1 1.2.5-r2 does not and that's probably the reason for this regression. The package in question uses standard find_package(ZLIB REQUIRED) macro, that correctly finds zlib, but the linking fails.
not a bug in zlib
Known problem, no fix so far *** This bug has been marked as a duplicate of bug 311147 ***