I have documents (facing pages) from 1 to 100. All of them have an anchored object that is relative to spine (left sided page shows object on left side of the page, right sided page shows object on the right side of the page). The page start location is on the right side.
The problem is that sometimes, I need to export pages FROM ONLY 2-99. This makes the anchored objects show up on the wrong side because it looks like PDF export doesn't take into account that page 2 has become page 1 in the export pages list subset.
If that's really happening it sounds like a bug.
How are you exporting to PDF, and how are you viewing? Sounds like you are exporting single pages, but viewing as spreads, and have the "cover page" option turned on...
what you get by exporting to PDF is no bug; it's totally logical, because you do not rearrange pages in your InDesign document to a new page order but by exporting to PDF. The anchored objects feature (relative to spine) is tied to InDesign pages not to PDF output.
So, if you want page 2 as the first page and a right hand one, you have to rearrange pages in your InDesign document before exporting.