Aassertion/deassertion masks (which are output parameters) are passed in the request as input data.
See baselib/oh_client.cpp:saHpiSensorEventMasksGet() and marshal/marshal_hpi.c: saHpiSensorEventMasksGetIn structure.
But if we fix it the RPC compatibility will be broken.
The problems will be between new client and old daemon
Decided not to fix it now to keep backward compatibility.
I leave this bug open for future.