Im pretty sure yaw hold is controlled only by the yaw gain setting and nothing to do with compass, the compass is used only in gps assisted modes and this does adjusts yaw to correct for wind drift. If your gains are set correctly then centering the yaw stick will hold its rotation in all modes including manual mode.
The naza still has atti mode even if a multi doesnt have a gps or compass unit installed so this should confirm the compass is only used for IOC modes, GPS mode and rth.
In ATTI mode the NAZA works as a gyro to self level the craft, it wont stop the current momentum or wind effects but it will auto level and keep drifting in whatever direction it was moving or the wind was drifting it. In GPS mode letting go of the stick will not auto level but pitch in any direction it needs to to hold position.
In manual mode letting go of the sticks will keep the phantom pitched at whatever angle it was at and the NAZA has no self leveling or position hold. In all modes though centering the sticks will not continue to pitch quad so this also applies to yaw rotation.