This is an auto-filed bug because sci-physics/hepmc fails tests. The issue was originally discovered on amd64, but it may be reproducible on other arches as well. If you think that a different summary clarifies the issue better, feel free to change it. Attached build log and emerge --info. NOTE: If you need further logs, feel free to ask.
Created attachment 642242 [details] build.log build log and emerge --info
Created attachment 642244 [details] other.tar.bz2 other logs
Fixed in version 2.06.11