Anti-Shake ON: 1 / 125 sec. Anti-Shake OFF: 1/160 sec.
The shutter sync speed is the highest limit of the shutter speed that the shutter can open fully. (For higher shutter speed than that, it becomes slit exposure and results in uneven exposure at flash photography.)
In this condition, the shutter run fully only for a moment and, if CCD shifts by the Anti-Shake, the there is a possibility that some part of the CCD is not exposed at all. To prevent this, the shutter speed is set longer to enable to expose the entire CCD.
(Considering the flash characteristics, with the shutter speed of 1/125 sec., serious exposure unevenness will not occur.)