It jumps to the right place for me in both directions.
It appears its a problem with my source. It indeed works with another (simpler) file. I'll check out.
After we sort this out, I would like to learn about the new "TeXShop Spotlight-based source/PDF sync".
Not quite so new, since version 2.0, I think. More information can be found in TeXShop Help. Advanced Help > PDFSync, more precisely. Apparently, it's based on search in PDF files. I think it's a feature included for Spotlight, I think.
Édouard