The current common_type implementation doesn't works when BOOST_COMMON_TYPE_DONT_USE_TYPEOF is defined. This is needed on platforms that don't support Boost.Typeof correctly.
It seems that the the implementation proposed by Jeffrey Hellrung has not been applied completly. I have attached a complementaty test on builting types that proves the current code does't works and also the implementation proposed by Jeffrey Hellrung to solve these issues some time ago.
John, let me know if this works for you and if it can be included on trunk (I could do it myself if you prefer).
Fixed header applied to Trunk as of rev 68040. I modified your tests somewhat and added updated test cases as well (with one case to test when BOOST_COMMON_TYPE_DONT_USE_TYPEOF is defined). Thanks! John.