dev-lang/perl installs the file /usr/lib/perl5/5.12.4/CPAN/LWP/UserAgent.pm while dev-perl/libwww-perl installs /usr/lib/perl5/vendor_perl/5.12.4/LWP/Useragent.pm the files are not the same and since the file from the libwww-perl contains the function new() and the file from dev-lang/perl does not I presume that that the libwww-perl one is the correct one (see cpan lwp documentation at http://cpan.uwinnipeg.ca/htdocs/libwww-perl/LWP/UserAgent.html#ua_LWP_UserAgent_gt_new_options ) It kinda escapes me why the same perl module is provided twice in different versions, though. Reproducible: Always
It's not the same module ( CPAN::LWP::UserAgent vs LWP::UserAgent ). If you want to use LWP::UserAgent then you must install libwww-perl.