title: Why does pikepdf fill-in some PDF fields but not others on a PDF created with Acrobat DC
body: <p>I have a PDF with form fields created with Acrobat DC by my customer. Using Python pikepdf I'm filling those fields programmatically. The strange issue is that some fields are filled, others not. I checked and double-checked with Acrobat DC: All fields have the exact same Text Field Properties, with the names obviously being unique. The Python code addresses the fields with their correct name. So I suspect that the problem might be related to the way my customer created the fields. Using Acrobat DC I deleted the offending fields and created brand new ones with the same Text Field Properties as the fields that show up as filled in  -- to no avail.</p>
  
  <p>Now I checked the pikepdf-generated PDF with Acrobat Reader, and all filled-in fields display their value, sigh! However, none of the Linux PDF viewers displays the content of the offending fields while displaying the content of some other fields. I tried Okular, Atril, the document viewer of XFCE4, and LibreOffice Draw. This seems to indicate that the issue on the Acrobat side of things. Any ideas?</p>