CompactLogix analog input is open, yet data says 20mA+

I am noticing odd behavior with a CompactLogix PLC I have here as a test unit. I have absolutely no I/O wiring on this unit, I just use it to debug code. I noticed that all the analog inputs are maxed out, which is opposite of what I would expect. In the config for the analog inputs, all four channels are enabled, set for 4-20mA, Engineering Units and are set to disable on open circuit. I would thus expect (and have seen in the field just last week at another site) that if the inputs are entirely unwired, the inputs should be showing no input and the scaled value I'm testing would be bottomed out rather than maxed out.

Any ideas why I'm observing this seemingly odd behavior?

Thanks!

Quick update: just for grins, I tried changing the "disable" on open circuit to "zero". The inputs did exactly that. Going back to "disable" on open circuit now has the behavior I expected: the inputs are bottomed out. Rather strange that they'd max out at first, but now I'm seeing the behavior I'm expecting.

When using rack based IF6I's and IF16's they show the exact same behavior. I'm not sure exactly why they do it but it drove me crazy the first few times. On the IF16's it usually alternates so that channel 0 is low, channel 1 is high, channel 2 is low, so on and so on. I'll I can guess is it builds up voltage somehow on a capacitor maybe?? with no load whatsoever connected. I've never really given it a ton of thought.