The voltage V� would ideally stay constant in the hold mode by having a value equal to Vin at the instance of clock going low. But there are two error sources due to switch:
1.The channel charge go to both junctions to causes negative glitches. If source impedance of Vin is small, then the glitch is small and last a short duration.
2.The channel charge go to V� causes a negative voltage that is long lasting.