Python XMP Toolkit: Remove ` lang="x-repair" ` from image description

Question

Summary:

I am trying to set the description of an image file using XMP metadata, with the Python XMP Toolkit (libxmp). I figured out how to do this, but for some reason, the string lang="x-repair" always precedes the description in certain programs. I'm an XMP noob, but I think it's due to the <rdf:li xml:lang="x-repair"> tag being interpreted incorrectly by the viewing/editing software. I need to find a workaround.

Problem Example:

Initial XMP (before adding description):

<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Exempi + XMP Core 5.6.0">
 <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
  <rdf:Description rdf:about=""
    xmlns:xmpMM="http://ns.adobe.com/xap/1.0/mm/"
    xmlns:stRef="http://ns.adobe.com/xap/1.0/sType/ResourceRef#"
    xmlns:xmp="http://ns.adobe.com/xap/1.0/"
    xmlns:photoshop="http://ns.adobe.com/photoshop/1.0/">
   <xmpMM:OriginalDocumentID>B4C00FF319085C77E5CD0403E55E459E</xmpMM:OriginalDocumentID>
   <xmpMM:DocumentID>xmp.did:7E6929740E3811EAA465CD5529117D4E</xmpMM:DocumentID>
   <xmpMM:InstanceID>xmp.iid:7E6929730E3811EAA465CD5529117D4E</xmpMM:InstanceID>
   <xmpMM:DerivedFrom rdf:parseType="Resource">
    <stRef:instanceID>xmp.iid:ab5c3c17-673a-4472-a464-5e81f92ba608</stRef:instanceID>
    <stRef:documentID>B4C00FF319085C77E5CD0403E55E459E</stRef:documentID>
   </xmpMM:DerivedFrom>
   <xmp:CreatorTool>Adobe Photoshop CS5 Windows</xmp:CreatorTool>
   <photoshop:AuthorsPosition>Contributor</photoshop:AuthorsPosition>
  </rdf:Description>
 </rdf:RDF>
</x:xmpmeta>
<?xpacket end="w"?>

Then I run the following to add a description:

my_image.xmp.append_array_item(libxmp.consts.XMP_NS_DC, "description", "This is a test.", {"prop_array_is_alt":True})

Now python says this is my current XMP:

<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Exempi + XMP Core 5.6.0">
 <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
  <rdf:Description rdf:about=""
    xmlns:xmpMM="http://ns.adobe.com/xap/1.0/mm/"
    xmlns:stRef="http://ns.adobe.com/xap/1.0/sType/ResourceRef#"
    xmlns:xmp="http://ns.adobe.com/xap/1.0/"
    xmlns:photoshop="http://ns.adobe.com/photoshop/1.0/"
    xmlns:dc="http://purl.org/dc/elements/1.1/">
   <xmpMM:OriginalDocumentID>B4C00FF319085C77E5CD0403E55E459E</xmpMM:OriginalDocumentID>
   <xmpMM:DocumentID>xmp.did:7E6929740E3811EAA465CD5529117D4E</xmpMM:DocumentID>
   <xmpMM:InstanceID>xmp.iid:7E6929730E3811EAA465CD5529117D4E</xmpMM:InstanceID>
   <xmpMM:DerivedFrom rdf:parseType="Resource">
    <stRef:instanceID>xmp.iid:ab5c3c17-673a-4472-a464-5e81f92ba608</stRef:instanceID>
    <stRef:documentID>B4C00FF319085C77E5CD0403E55E459E</stRef:documentID>
   </xmpMM:DerivedFrom>
   <xmp:CreatorTool>Adobe Photoshop CS5 Windows</xmp:CreatorTool>
   <photoshop:AuthorsPosition>Contributor</photoshop:AuthorsPosition>
   <dc:description>
    <rdf:Alt>
     <rdf:li>This is a test.</rdf:li>
    </rdf:Alt>
   </dc:description>
  </rdf:Description>
 </rdf:RDF>
</x:xmpmeta>
<?xpacket end="w"?>

BUT! Once I close the file (write XMP) and open it again, it says this is my XMP:

<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Exempi + XMP Core 5.6.0">
 <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
  <rdf:Description rdf:about=""
    xmlns:xmpMM="http://ns.adobe.com/xap/1.0/mm/"
    xmlns:stRef="http://ns.adobe.com/xap/1.0/sType/ResourceRef#"
    xmlns:xmp="http://ns.adobe.com/xap/1.0/"
    xmlns:photoshop="http://ns.adobe.com/photoshop/1.0/"
    xmlns:dc="http://purl.org/dc/elements/1.1/">
   <xmpMM:OriginalDocumentID>B4C00FF319085C77E5CD0403E55E459E</xmpMM:OriginalDocumentID>
   <xmpMM:DocumentID>xmp.did:7E6929740E3811EAA465CD5529117D4E</xmpMM:DocumentID>
   <xmpMM:InstanceID>xmp.iid:7E6929730E3811EAA465CD5529117D4E</xmpMM:InstanceID>
   <xmpMM:DerivedFrom rdf:parseType="Resource">
    <stRef:instanceID>xmp.iid:ab5c3c17-673a-4472-a464-5e81f92ba608</stRef:instanceID>
    <stRef:documentID>B4C00FF319085C77E5CD0403E55E459E</stRef:documentID>
   </xmpMM:DerivedFrom>
   <xmp:CreatorTool>Adobe Photoshop CS5 Windows</xmp:CreatorTool>
   <photoshop:AuthorsPosition>Contributor</photoshop:AuthorsPosition>
   <dc:description>
    <rdf:Alt>
     <rdf:li xml:lang="x-repair">This is a test.</rdf:li>
    </rdf:Alt>
   </dc:description>
  </rdf:Description>
 </rdf:RDF>
</x:xmpmeta>
<?xpacket end="w"?>

As you can see, libxmp seems to have added xml:lang="x-repair" to the tag containing the description text. For some odd reason, some programs seem to read this with a literal lang="x-repair" prepended to the description text. I've tried both GIMP and the Ubuntu built-in file properties menu, with the same erroneous results. However, various online metadata viewers predictably do not have this problem.

My Question:

Is it possible to add a description to an image using the python libxmp module WITHOUT automatically adding the xml:lang="x-repair" part? I think this would effectively work around the text rendering bug I've found in various programs.