Ok. Here goes my try at answering your question.
I used 2001 to do all my simulations so bear this in mind just in case it may be more of a version specific problem.
I hooked up the circuit with 3.3 Volts running to the Anode of the Opto-coupler through a switch and 27 ohm resistor. I then connected the collector of the internal transistor straight back to the 3.3 Volt source. When I first tried this the Voltage at the emitter stayed at 3.3 Volts at all times. I then added a 1K resistor from the emitter to ground and then the voltage swung from real low (uV range) up to 3.03 Volts.
If the above description fits what you were seeing then it is apparent that a resistor must be attached to the emitter of the transistor in the opto-coupler in order for it to function as it should. This may be the case (and I believe that it is) for the real component.
I hope this helps. If not let me know and I can post my model for this particular opto-coupler for you to try.
