Analog switch transient behaviour

I am using an ADG719 analog switch (see circuit). I have a fixed voltage of 4.5V on an input and 0V on the other. I am switching between the inputs at 125kHz. If I look at the switch output I see some form of transient behavior (see image). It takes about 150us before the output values are in a steady state. Before that the values seem to ramp up (if you look at the top cursor the first values are at a lower level than the later ones). Does anyone know what would cause this?  I am guessing it must be something to do with the input of the buffer amplifier on the switch output.

Thanks for any help.