Posted a Bug Report here: Ticket #8937 https://svn.boost.org/trac/boost/ticket/8937

Seems like a bug/feature of Windows 7/Vista (or a bug/feature of Windows socket subsystem) - something in background/foreground process scheduling or a memory management issue. Nevertheless it is interesting to know the Asio author's point of view. It will be more clear if the topic starter rewrites his (simple) examples to use WinSock directly rather than through the Asio (use the same time measurement - by means of boost::posix_time). I think that such rewritten examples will show the same behavior. Regards, Marat Abrarov.