The background images here don't give me any trouble, but the other bugs do occur:
https://www.chaosium.com/content/Fre...Quickstart.pdf
The background images on some Bundle of Holding pdfs have been making things unreadable, but I shouldn't share them.
Splitting individual pages actually helps with this-- at one point I was running cpdf to split, ghostscript to convert to 1.4, ghostscript again to remove images and vectors, cpdf to merge, and cpdf to blacktext. But using ghostscript again would cause some of the same errors to reappear.