Senior Cinco I also have this problem. My thread:
http://www.larian.com/forums/ubbthreads.php?ubb=showflat&Number=453822&gonew=1#UNREAD

What I have found is, once game is relaoded.. go straight to gameplay, move adjustable difficulty to "hard", then litterally move it straight back to "nightmare".. it will ask if you are sure. hit "yes" and the enemies are full HP and back to nightmare standard difficulty. Annoying, but works.

I dont know if people are also experiencing this as well...
Enemies keep walking away during battle.. my summoned creature does this also at times. Its annoying as my creature will leave the fight and just start walking towards me (im shooting arrows from a little distance away) and getting killed. Enemies also are making the "nightmare" setting a little dissapointing at times as when they are walking back they wont retaliate to me hitting them with everything I have got. frown