Maybe someone is able to explain this behavior: Played around with some photos in LR (very pleasant and warm autumn day and a even better sunset) and the histogram seems to act rather odd. Everything looks quite normal reducing exposure (german: Belichtung). The "hill" slides gently to the left and the "peak" keeps its height ... until ... I cross a border and the "hill" losing half its height.
Reducing exposure any further doesn't seem to affect the height. It keeps the reduced level..
LR 3.5 (64 bit)
Windows 7 Ultimate (64 bit)