Why am I seeing comments from one PDF-based assignment in another?!

This is a "known issue" that stems from how PDF (Portable Document Format) files are encoded.  In some cases, if a PDF file shares common characteristics with another file - even a file with a different name! - this may confuse Hypothes.is, who tries to treat both links as pointed at the same document.  For example, this can happen if you created a single PDF file and subsequently decided to break it into two PDFs.  

To solve this problem, try creating PDFs one at a time.