As per #595376, A user reported needing to rebuild icinga manually after upgrading Perl. As the code indicates it links against Perl, then a rebuild is indeed indicated, and a subslot recommended.
commit 6f1d011e30dbce0eab4052d9960e486e1c6352bf (HEAD -> master, origin/master, origin/HEAD) Author: Andreas K. Hüttel <dilfridge@gentoo.org> Date: Thu Sep 29 23:27:21 2016 +0200 net-analyzer/icinga: Add missing slot operator in Perl dependency, bug 595428 Package-Manager: portage-2.3.0 net-analyzer/icinga/{icinga-1.13.3-r1.ebuild => icinga-1.13.3-r2.ebuild} | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)