Otherwise we get, i.e.,: WARNING: One or more updates/rebuilds have been skipped due to a dependency conflict: app-text/podofo:0 (app-text/podofo-0.9.6_pre20171027:0/0.9.6_pre20171027::gentoo, ebuild scheduled for merge) conflicts with app-text/podofo:0/0.9.6_pre20170629[boost,idn,-debug,-test,tools] required by (virtual/podofo-build-0.9.6_pre20170629:0/0.9.6_pre20170629::gentoo, ebuild scheduled for merge) As a quick-and ditry test, cp ${PORTDIR}/virtual/podofo-build/podofo-build-0.9.6_pre2017{0629,1027}.ebuild resolved the dependency problem on my ~amd64 and seemed not to cause anything terrible to happen insofar as I could still build and run calibre after updating.
*** This bug has been marked as a duplicate of bug 637290 ***