Switched capacitors using MOSFETs in filter design
"Can anybody tell me what I'm doing wrong here?"

Yes - I am afraid you didn´t realize that in the second circuit (MOSFET realization) the capacitor C2 now is operated with phase inversion. That means: The most right opamp now is operating as a non-inverting integrator (besides all other effects as mentioned already).

As a result - you have positive feedback, in contrast to the first circuit (with idealized switches and another S/C realization). You can cure the situation by modifying the clock sequence for two switches.