UPDATE - Problem solved!! Yes, you can lock fob in the truck both with it running and with it shut off. I remembered I had BOTH keyfob

 

Sorry... Both key fobs in truck and thought maybe that was it. Well, I took one out and now it will lock. Go figure... No clue why this would make any difference.

 

Great - You had me nervous as I love this feature. No clue why it did that...

 

I think you are one of the like.. 3 that have their 2015 already

 

When you took one out and locked it... was the other one (not in the truck) on you? Or was it like 10'+ away?

 

Though in reality, not sure why I'd ever take the keyfob out of my pocket... I don't now on my G35...
And another benefit I love of the securicode... you can unlock your truck without your keys. I have it on my Explorer and use it all the time to go grab something out of vehicle and forgetting the keys.

 

In my pocket

 

That's not valid then... since you had one on your of course the doors will lock.
Leave one in truck with no others on you or near the truck. My guess it won't lock (same as having both in the truck).

 

...guess again

 

If it operates the same as my MKX, the horn will beep on the first attempt to lock it (warning you there's a set of keys inside). A second press of the lock button will indeed lock the doors with the keys inside.