LT1009 open loop simulation

Good Morning!!

I am kindly asking the community to understand what can happen when LT1009 precision reference is simulated in open loop. 

You can see the schematic simulated below:

And the result I get is:

I'm expecting the behaviour showed in the image below. Whenever the input signal (blue) overpasses reference voltage (2.5V) the output (red) goes from 5V to 2.5V (Vref)

It's quite strange since it is correctly working in closed loop in other simulations I have but I can't figure out what's happening. The current usage it has is as a comparator and in fact, in the real PCB the circuit is properly working.

Thanks a lot in advance for your kind support.

Best Regards,

Jose