Why does a pdf imported into LibreDraw show extra objects?

Unfortunately I cannot upload a file without 3 points, otherwise I would attach it to this question, but when I open a PDF in LibreDraw, I get a bunch of checkered objects covering parts of the PDF. I then have to go through and remove the checkered objects to be able to work on the PDF content that is underneath them. Is this a bug, or can this be fixed via a setting?