ISSNs contain extra punctuation

[osma]

I noticed a minor issue when converting records containing ISSNs. For example, the second record from this batch of two records has a 490 field containing an ISSN:

    <marc:datafield tag="490" ind1="1" ind2=" ">
      <marc:subfield code="a">Jyväskylä studies in humanities,</marc:subfield>
      <marc:subfield code="x">1459-4323 ;</marc:subfield>
      <marc:subfield code="v">187</marc:subfield>
    </marc:datafield>

The ISSN gets converted into this BIBFRAME2 RDF/XML:

        <bf:identifiedBy>
          <bf:Issn>
            <rdf:value>1459-4323 ;</rdf:value>
          </bf:Issn>
        </bf:identifiedBy>

Notice that the rdf:value still contains the space and semicolon. I would expect these to be stripped as they are not really part of the ISSN code.