Searching for HTTP::Headers::UserAgent returns version 1.00, belonging to JNEYSTADT.
If I search for the same module name on search.cpan.org, I get version 3.01, belonging to IVAN.
That seems to be fixed. Here is a link: https://metacpan.org/module/HTTP::Headers::UserAgent
Just for the record: it turned out this was an issue on CPAN: it was confused between the two versions.
I resolved it by getting co-maint and uploading a new release.