Comparator Output from item frame not working at all

So this is a head scratcher: I was playing around with Item Frames and Comparators. The first set up worked fine. I placed an item frame with a redstone torch within the frame upon an iron block. On the opposite side, a comparator set to compare. At the original position, the comparator outputs 1 power. Each click of the item frame increases the power by 1. This is exactly how I expected this set up to work.
However, if I repeat the set up anywhere else, the comparator will output nothing. I can remove the first function set up and reinstall it. It only works in the exact position that I originally set it up in. I have restarted the map and the program. I have gone into other worlds to try... it still doesn't function. Any idea what is going on?