The below is the circuit in question using LTSpice XVII(x64) (18.104.22.168)
The two sources have the exact same sine wave, just with different DC offsets. One with a DC offset of 5V, the other with 0V.
So, when you subtract, or measure the voltage between Vcc and Vref, you should get a perfect DC value. And we do. But, when you measure the voltage between Vdiv and Vref, it has some AC signal.
I'm going to assume there is a setting or a way LTspice functions that I don't know about.
Here is the output measuring the voltage between Vcc and Vref. A perfect 5V DC
Here is the output measuring the voltage between Vdiv and Vref.