I have the circuit as shown in the below attached image. I am giving 125 KHz(sine) signal through buffer to the switch and at the same time i have 125KHz square wave with 0 to 2.5v to the switch input. I am measuring the voltage at point "Vout". I am getting some glitches or extra peaks when the switch is changing. When the switch going "on"to "off" i have 12v glitch or peak. When switch is going from "off" to "on" then i have small peak. I have attached the image of oscilloscope for clear representation how the signal is look likes.
Supposing you left switch unterminated and attaching only oscilloscope probe to it's output may be the reason for those problem you have. Switch capacitance when opened is in range of 30pF and passes signal to output.
Switch must be terminated with proper load impedance.