Why won't Photoshop cover the hotspot on the forehead using the clone stamp tool? There are pixels there; it's not transparent. I've run into this before, which Photoshop refuses to paint or clone stamp over a hot spot.
What is set from Sample drop down list in the Options bar? This can be problem if you are on new blank layer and option is set to Current Layer. Another option is Current and Below which also can cause problem.