in tb109reviews-xie, there is a spurious _ in the visible text of reference [7]:
http://tug.org/TUGboat/tb31-_2/tb98ziegenhagen.pdf
although the target of the link is correct (no _).
Input from bbl was just:

\newblock \url{http://tug.org/TUGboat/tb31-2/tb98ziegenhagen.pdf}.

Boris also mentions:

]the # character] in URLs is not
translated properly, so I [need] to write something like
\href{../index.html\#xie-knitr}{\bookinfo} instead of
\href{../index.html#xie-knitr}{\bookinfo}