[boost] [serialization] Assertion while serializing polymorphic type through pointer to base class

Hi all, I'm trying to serialize a polymorphic type through a pointer (shared_ptr) to a base class and I'm getting an assertion deep inside the library here: archive/detail/oserializer.hpp, line 417. I'm using V1.34.1 for this. Is there anything known about this assertion? Anything obvious I'm missing? Regards Hartmut