So me and my friends tested it out about 3 separate time. When "Lord of Winter" is casted within the guild house the graphical client crashes. According to the dump file it uses up 35% of my ram. The cause of this in unknown. Using "Lord of the Winter" outside of the guild hall doesn't seem to have lasting effects. But I'd advise for the time being not using "Lord of the Winter" or any variations of the spell in the guild house less it crashes your game.
There's another thread about this under bugs section of the forums - this is not just happening when the spell is cast in the guild halls, this is also happening in various areas of the game - I had it happen in Azteca when Blue Agnes cast this spell on me. It is specifically happening with this spell. If you're an Ice or with an Ice, someone else suggested packing Melt in your deck to try to dispel it before it's cast.