LT1167 in LTSpice


I tried to build EMG sensor based on LT1167. I found typical application (figure 8) and try simulate it in LTSPICE.

AC Analysis looks ok but something weird happen in trans.

After first filter (Highpass - red wave) it looks ok but after second filter it gives me square wave. Why this is happened? Is suppose to just gain in this frequency. Maybe I don't understand what going on in circuit.