Latest upstream version is 4.1.5, in portage is 4.1.4. Assigning to you, mrueg, because you committed the latest ebuild. There's a maintainer with a non-gentoo-address listed in metadata.xml who apparently has no bugzilla account. This probably should be resolved somehow, he would be a proxy maintainer then, but should definitely have a bugzilla account, so bugs can be assigned.
The reason you couldn't find it, is that it's an upstream liason. The package itself is unmaintained, I bumped it. commit 143a505c0252008fd378881e1e3a066b4a0c0243 Author: Manuel Rüger <mrueg@gentoo.org> Date: Mon Aug 22 20:03:14 2016 +0200 net-libs/zeromq: Version bump to 4.1.5 Gentoo-Bug: 591560 Package-Manager: portage-2.3.0