A friend (@ViciousCabaret) of mine (@Michelle Angelmark) was the only controller on a Manticore Task Force, and found that they were unable to hold Paragon Protector bosses, even when stacking multiple casts of [Blind] on them. They asked me to check with my own Illusion controller if things were working normally, and with [Power Analyzer] I found that casts of the same hold no longer stacked magnitude - the first hold 'wears off' as soon as the second is cast, even if the first one would have lasted for an entire 30 seconds longer if I had just waited (and did last 30 seconds longer when I did wait after holding it on the exact same mob). This renders Controllers, or at least Illusion Controllers using Blind, unable to hold bosses without getting a proc. Is this intended behavior? It seems significant enough that I think it'd be mentioned in a patch.
Edit: Three controllers on Everlasting, local names Patric.AI, Pierrette, and Kakadu, tested this on several bosses. The same power cast by different people does stack magnitude on the same boss, but the same power cast by the same person only resets the duration rather than stacking. Officially, I'm not *opposed* to this change - as someone with a Mind Dominator main on Live, crowd control is ridiculously overpowered in this game - but this seems like a major change that I doubt would be intentionally pushed with no discussion.