Kia ora JC!
This does seem like something happening on the NCBI’s end. Playing around a little, it also effects “normal” (that is, non web-history queries). I don’t think sending one ID and getting back 8 records is an expected behaviour, so it’s worth letting them know about it.
Depending on what you want to get from the records I can suggest at least one workaround for now. If you download records in “gbc” format, which is a XML-ficaton of genbank you do get one record per ID. You can’t return a parsed object (for now, I’ll start an issue for this and other cases where XML records are not called XML), but it’s easy enough to create one and retrieve information from it:
seqrecs_gb_xml <- entrez_fetch(db="nuccore", web_history = seq_NZ$web_history,rettype="gbc")
parsed <- XML::xmlTreeParse(seqrecs_gb_xml, useInternalNodes=TRUE)
<INSDSeq_taxonomy>Eukaryota; Fungi; Dikarya; Basidiomycota; Agaricomycotina; Agaricomycetes; Agaricomycetidae; Agaricales; Lyophyllaceae; Gerhardtia</INSDSeq_taxonomy>
Hope that helps, and let me know if you have other questions.
EDIT to add a link to the issue regarding parsing differently named XML files on the fly: Rentrez - problem using the web_history object