I work for an Australian airline that flies A330-2/300. We have experienced this issue and found air flows fwd from fwd lav into flight deck behind sidewall due to airflow issues. This is due to a restriction to the Lav vent extraction system. We have had the restrictor in the fwd lav extraction duct removed and this seems to solve the problem as there is now a greater airflow into extraction system with restrictor removed. Air is thus no longer moving fwd into flt deck but upwards into lav vent system. Our reports go back as far as 2003 and Airbus are aware of the issue.
