I'm not sure if this is a issue or if it will ever be. I'm not sure and I'm just going to record this as a event and keep and eye out to see if it happens again and under what circumstance. But I was running CoT - Stratholme and Utgarde Pinnalce with included a Death Knight in party and noticed I kept running low on mana.
Low enough that if I remember correctly I was popping Devine Plea and Arcane Torrent constantly for mana when off cooldown. I couldn't figure out why at the time. But I never stopped to drink though as i just rolled with it. At times I had to change seals to using SoW. On most my instance runs I've so far never had any real mana issues at all usually.
But in CoT - Stratholome I kept having it this one instance as well as I did notice it in Utgarde Pinnacle with another Death Knight in party. I kept running low on mana with BoS up. Now the only thing I can figure so far is some Death Knights using Death and Decay often as AE without regard to how the current Tank (Paladin) in the group Tanking mechanics work. Thus causing Threat over the Tank threat and reducing the mobs hitting the Tank (Paladin) who does need the reactive threat and for BoS to proc for mana.
Thus at times that may be the problem I have encountered, which may be due to how some Death Knights are playing their class at the moment. I'm currently unsure at the moment and may need some feedback on this since I've never really played a Death Knight. Mine is still sitting on ice. But at this point i'm not sure if this is a issue or can be one with some new Death Knights in groups with other Tanks in how they usually Tank.