I don't know why Anti-Ice would change IAS... Whether or not we turn it on (747), target speed is the same. The only difference is engine N1.
Gusty winds are the likely answer here. If the OP is reading IAS, wind gusts will cause significant changes in IAS. The knowledge of wind gusts will also cause the Pilot to adjust target speed upward on final.
I have better things to do than turn off Anti-Ice on final, especially when the winds are not steady. If it is ON at the Approach Checkilst and the ground temp is +4, it will likely stay on. Clearing clouds after the Landing Checklist will not change a thing.