/bin/zcat-reference and /bin/gunzip-reference are shell scripts. They call exec gzip. This is a problem if gzip's symlinked to pigz, because it's expected that reference means app-arch/gzip not app-arch/pigz.
Steps to Reproduce:
1. Have app-arch/gzip installed and app-alternatives/gzip[pigz] set.
2.try to zcat some crap pigz can't handle like some old abandonware
cat share/lotus/123.v10/sysV386/lib/123.o.z_1 share/lotus/123.v10/sysV386/lib/123.o.z_2 | zcat > test.o
zcat: skipping: <stdin> unrecognized format
reference implementations point to reference gzip, not pigz.
I'd patch this myself but I think it has to be done early in case users have a weird system not installing to /bin.