"Print only" Watermark made visible on screen by Adobe Sign

I added a Watermark to a PDF document in Adobe Acrobat DC and set the Appearance option "Show when printing" checked and "Show when displaying on Screen" unchecked.  The Watermark behaves as intended and is only visible on the printed document. 

However, if the document is Signed using the Fill & Sign option (i.e. Adobe Sign), the Watermark is now visible when the (signed) PDF is displayed on the Screen.

It would appear that by uploading the document to Adobe Sign the Watermark Appearance options are changed, or ignored?!  Is this a bug, or is there a valid reason for this behaviour?