I had the same problem with Writer 3.6.3 where none of my previously pinned Writer documents would show up on the jumplist. I also was not able to repin any of the documents.
I finally tried to resave my Writer document with the .odf extension, the extension it recommends when trying to save to .docx, and for some reason it worked, and without any of the formatting problems I had with the .docx format.
Hopefully that helps for those of you with Writer document pinning problems. That said, it still would be nice to be able to pin normal .odt files.