[boost] Teeks GCC test failures - multiprecision, spirit and others

There are a lot of inscrutable failures from the Teeks machines running GCC on linux that I'm unable to reproduce (and aren't reproduced by other testers), for example: http://www.boost.org/development/tests/develop/developer/output/teeks99-03d-... All the failures refer to is_convertible, and have an instantiation back trace that leads nowhere (a line that doesn't instantiate anything, and which refers to Boost.Range which multiprecision doesn't use). I see similar failures in the spirit tests as well. Is anyone able to reproduce these? Any ideas what may be going on? The failures are on the master branch as well if that helps. Many thanks, John.