I've tried recompiling some complex documents meant for pdfLaTeX using XeLaTeX. After a few fixes and
\ifxetex in the preamble (regarding input, hyperref and font encodings), it went through... but for some reason the newly produced document was 117 pages long instead of the original 115!
The reason is that a blank double page (well, blank except for running headers) is inserted between chapter 3 and 4.
Obviously, this is something difficult to reproduce - it did not occur between all chapters, and it possibly depends on the height of the last page.
Does this resemble some known phenomenon?