Observer Block Not Detecting Movement of Item in Item Frame/Comparator Strength Change

When a comparator has a different signal strength then before, the observer block does not notice it. In versions prior to 16w 44a, when you had an item in an item frame, have a comparator behind it, and then a observer block, it would detect the signal strength change when you rotate the item around. Not sure if this was a bug before 16w 44a, or is now a bug.