as described in issue 112652, for certain formats the number formatter
may insert a decimal separator (comma) into doubles that are NaN.

i.e. the result is "N,aN".

this seems to depend on the style used, from the bugdoc:

    <number:number-style number:language="hu" number:country="HU"
style:name="N5002">
      <number:number number:min-integer-digits="1" number:decimal-places="2"/>
    </number:number-style>
    <number:number-style number:language="hu" number:country="HU"
style:name="N5000">
      <number:number number:min-integer-digits="1"/>
    </number:number-style>

the problematic style seems to be the first one.