Neither incorrect optimization in the 64-bit compiler (as it was in the Sigurd's case) nor misoperation of the serialization library in multithreaded environment (as it is noticed by Robert) was a reason.
Hmmm - I thought you were all the same person.
The reason was very simple: in one of the classes the BOOST_CLASS_EXPORT macro was used before inclusion export.hpp, that led to the class registration code was not instantiated.
Note that in the most current version of serialization, checked into the HEAD, instantiation of code has been improved by D. Abrahams. Its possible that in the future this would never have occured.
Thanks, Sigurd and Robert, for your time. Though your replies have not pointed to the real reason, they pushed me to think in another direction and eventually to resolve the problem.
You're welcome. I'm always happy to send someone off in the wrong direction.. Robert Ramey