Did Feral Charge always interupt casting or is that new? I know that it has always stopped movement for a second but I dont remember it interupting spells. Either way I am loving it.

It has interrupted casting for as long as I can remember, but I didn't create my druid until about 9 months ago.

It always has, and always should do :) Also prevents them from casting for a certain time as well ...

Its a spell interrupt and basically, a silence for whatever school of magic it was from. So if your fighting a frost mage, and you feral charge his frostbolt, you basically just shut down his system for a good few seconds.