If you click a title in the OPAC cart, it will create a URL like the following:

http://localhost:8080/cgi-bin/koha/opac-detail.pl?biblionumber=114?biblionumber=114

This is because of competing functionality in the template and the Javascript. The output of the following "biblio_a_href" is fed into "openBiblio". 

koha-tmpl/opac-tmpl/bootstrap/en/includes/html_helpers.inc
[% BLOCK biblio_a_href -%]
    [%- IF Koha.Preference('BiblioDefaultView') == 'marc' -%]
        [%- SET this_biblio_href = "/cgi-bin/koha/opac-MARCdetail.pl?biblionumber=" -%]
    [%- ELSIF Koha.Preference('BiblioDefaultView') == 'isbd' -%]
        [%- SET this_biblio_href = "/cgi-bin/koha/opac-ISBDdetail.pl?biblionumber=" -%]
    [%- ELSE -%]
        [%- SET this_biblio_href = "/cgi-bin/koha/opac-detail.pl?biblionumber=" -%]
    [%- END -%]
    [%- this_biblio_href | url %][% biblionumber | url -%]
[%- END %]


koha-tmpl/opac-tmpl/bootstrap/js/basket.js
function openBiblio(dest,biblionumber) {
    var openerURL = dest + "?biblionumber=" + biblionumber;
    opener.document.location = openerURL;
    opener.focus();
}