I don't know if the "Can cast 2 spells per round" works for other people but when I equipped it. I was casting exactly the same number of spells per a turn as the character that was not using the sword. I ended up doing some research on the effect: Increase spells cast per round (188). This thread says that the effect can only turn off the cool down not actually determine the number of casts per a round.

If anyone else knows a ways to make the sword function correctly, I would appreciated any help.

thanks