When one emerge t1lib-5.0.0 then no /usr/lib/libt1.so.1 will be created. Therefore, some apps (e. g. xpdf) won't work anymore.
Try t1lib-5.0.0-r1.ebuild and use revdep-rebuild to rebuild everything depending on t1lib.
That fixed the problem, I consider this bug as fixed.
Thanks for testing. I removed t1lib-5.0.0.ebuild and added warnings to t1lib-5.0.0-r1.ebuild to make sure people rebuild packages depending on t1lib.