If we have a scheme like so, with default lengthKind="delimited"

<xs:element name="root1">

  <xs:complexType>

    <xs:sequence dfdl:separator=";">

      <xs:element name="one" type="xs:string" />

      <xs:element name="two" type="xs:string" />

      <xs:choice>

        <xs:element name="c1" type="xs:string" />

        <xs:element name="c2" type="xs:string" />

      </xs:choice>

    </xs:sequence>

  </xs:complexType>

</xs:element>

And the infoset:

<root1>

  <one>

    <foo>1</foo>

  </one>

</root1>

Then we end up getting into StringLengthDelimited trying to cast a DIComplex (one) to a DISimple. Of course one should be a simple type, but it's not in the schema and we aren't doing a check somewhere the ensure it is a simple type. I don't think this is a problem with StringDelimitedUnparser, but somewhere else (maybe in the InfosetSource or NextElementResolver?)

See test_unexpectedChildNone in daffodil-test/src/test/scala-debug/edu/illinois/ncsa/daffodil/unparser/TestInfosetDebug.scala