Now I * downloaded the python 2.75 source * compiled python 2.75 * compiled boost 1.54 against python 2.75 * built our software against these new libs -> The behavior is still the same. ob_type of the first python object I create is 0xffffffff, and trying to access it results in an immediate crash. This only applies to the debug version. Release is fine. Also, the behavior is the same, if I link the boost debug build against python release or debug. Rgds Richard