I played most of the evening last night, and found that my ultimates remained at approximately a 90% level without moving. This was particularly painful when I faced some formidable bosses . Perhaps this isn't the right place to post this, but I was really hoping to gain some insight, since I'm still befuddled as to how ultimates charge up in the first place.
Some guildmates suggested that this happens when you're approximately 5 levels above the zone's general level, which was actually true for me. I really can't help that though because I'm somewhat fastidious in trying to do everything, and I end up leveling past the zone, and, of course, this stacks up as you move further up through the zones.
So I guess one thing I'm trying to determine is whether this is a purposeful mechanic, or is it a bug.
Just a side note, my ultimates did charge up all the way when I went up against some daedric invaders (you know, the dark blue cloud thingie that occurs from time to time).
Thanks for any insights!