It looks like the erlang and zlib formulae are both trying to install a manpage to the same path:
$ brew link --overwrite --dry-run erlang
$ ls -l /usr/local/share/man/man3/zlib.3
lrwxr-xr-x 1 username admin 48 7 Mar 09:27 /usr/local/share/man/man3/zlib.3 -> ../../../Cellar/zlib/1.2.7/share/man/man3/zlib.3
Yuck, erlang shouldn't be shipping zlib man pages...
They're different man pages. The one installed by zlib is for the library itself and the one installed by erlang is for the erlang zlib API.
Surely they were aware "zlib.3" is taken.
Considering erlang installs hundreds of man pages (632 according to brew list erlang) they should probably be going into a separate section. Perl installs man pages in 3pm, openssl installs them in 3ssl, pcap in 3pcap, etc.
brew list erlang
I agree, at the very least they should provide a configure option to set the man page extension.
We've reverted to Erlang 15 for the time being, so shrugging this off until we move forward again.