Changes made to a particular space's PDF stylesheet reflects on the others'. Hence, virtually every space is using the same PDF stylesheet.

Quoting CSP-43577 (restricted from public):

• We have used a custom stylesheet for PDF exports that seemed to work fine so far. We copied this stylesheet to every space to ensure that the exported PDFs look the same for every space.
• When I change the stylesheet in one space, I see these changes in every other space.
• In some spaces, I can change the PDF stylesheet, but nothing happens. The PDF still uses an older stylesheet version. But it does not use the default stylesheet, even if I delete the stylesheet configuration completely.

This behaviour does not appear in Confluence 3.1 (PDF Export Plugin v1.3)