Steps to reproduce:

1. Create a page with special characters (e.g., C++ Page) so that editing the page shows the page id instead of the page name
2. Attach an image to that page
3. Export space to HTML (attached images are duplicated, once under [page name]_attachment and once under page id)
4. Rename page so that it does not contain special characters (e.g., CPP Page)
5. Reexport space to HTML (attached images are still duplicated for all pages!, once under [page name]_attachment and once under page id)