This ebuild doesn't install /usr/share/bash-completion/helpers/perl which is required for /usr/share/bash-completion/perl (btw, this helpers/perl file must be also executable). You can test this using: $ perldoc Get<Tab>
*** This bug has been marked as a duplicate of bug 520030 ***
oops, not a duplicate
+ 06 Sep 2014; Michał Górny <mgorny@gentoo.org> bash-completion-2.1-r2.ebuild: + Install helpers needed for completions as well, bug #520032. Fixed it while the new revision is still hot.