Are you sure you're not getting more than one boost library in your executable then?
I've managed to do that before (with MSVC, not MinGW), and those bugs can be a PITA to find.
Do you mean more than one version of the same library, e.g., debug and release? If so, I'm fairly certain that's not happening (the build commands used are in my first post, and only one version of the Boost Thread library is linked). However, if I've misunderstood you, please let me know; I did have to manually define BOOST_THREAD_USE_LIB in my own program to use static linking for the Thread library (see https://svn.boost.org/trac/boost/ticket/4614), which seemed a bit off, so it's possible there's something going wrong there (although I'd expect it to affect the other aspects of the Thread library as well). William