Can you say how you measured this? What function you patched, what the code was, etc.?
I was checking 'Cite::referencesFormat-parse' profiling hook, as it is prominent on generic profiling, is not reentrant, and can be easily isolated in ?forceprofile=true outputs like here:
http://en.wikipedia.org/wiki/Rod_Blagojevich_corruption_charges?action=purge...
(you have to be logged in, view source).
BR,