Duplicate headings can lead to broken internal links in the generated PDF

Follow these steps to reproduce:

• create a parent page with some content (doesn't matter)
• create a child page with this content:

  == Description ==
  
  Description of the first item. Checkout the [[Usage section>>||anchor="HUsage"]] for more details.
  
  == Usage ==
  
  This is how the first item is used.
  

• create another child page with this content:

  == Description ==
  
  Description of the second item. Checkout the [[Usage section>>||anchor="HUsage"]] for more details.
  
  == Usage ==
  
  This is how the second item is used.
  

• export the parent page to PDF, along with its 2 child pages; make sure the table of contents option is checked

Result: the heading links in the PDF table of contents are fine, pointing to the right print page, but the 2 section links within the PDF content are pointing to the same print page (i.e. both point to the first "Usage" section).