Image alternative text is lost when Word document is converted to PDF using VB.NET

I’m saving a Word document to PDF. During this process alternative text set for the shape is not ported to PDF.
Dim map As Image = Image.FromStream(mstr)
Dim mapImage As Image = map
Dim mapShape As Shape = builder.InsertImage(mapImage)
mapShape.AlternativeText = "test"

Am I missing something here?

@CFPratt

Thanks for your inquiry.

I managed to reproduce this issue on my side. For the sake of correction, I have logged this issue in our bug tracking system. Your request has also been linked to the appropriate issue and you will be notified as soon as it is resolved. Sorry for inconvenience.