[Koha] Using build_oai_sets.pl with embed items option

Hello all, I've configured an OAI set mapping with the field 995$a equals "libcode", where 995$a holds the aquisition library code for the item. As this is an item field, not a biblio field, I have to run build_oai_sets.pl with '-i' option in order to embed items to the records. This is working fine, however, it's only indexing records which only have 1 item of 'libcode'. Every other biblio with, say, 5 items from different libraries and 1 from 'libcode' library are not indexing. I think the C4::Biblio::EmbedItemsInMarcBiblio function might be only considering the first item in a biblio, instead of checking all of them. Has anyone else come across this situation? Thanks, Pedro Amorim