EPUB2 is really complex and it gets worse with EPUB3. So far I have not seen a single software which could flawlessly process all EPUB2 files. The fact that Pocketbook was able to show some particular EPUB file which Sony (which uses Adobe RM SDK) fails to process does not give you a guarantee that with some file it would not happen the other way around
By the way - in your sample there are several <pre> blocks, but none of them has a single space character...