Better gloves lowering my stats.

Here is the situation :
I am playing on my level 16 Witch, and I have some

Superior Rawhide Gloves equipped (Quality : +16% ; Evasion Rating : 13)

On them I have put 2 blue gems, which are :

Fireball, level 6
Added Lightning Damage, Level 1

By looking at my Fireball spell, I have a DPS of 70,3 and a Cast Time of 0,84s

Now I equip a better glove that I have just looted :

Doedre's Tenure Velvet Gloves (Energy Shield : 28 ; 43% Increased Spell Damage ; +10 Intelligence ; 20% Reduced Cast Speed ; +16 To Maximum Energy Shield)
I also put the same gems on this glove.

Logically, I should now have more power, a better Fireball.
Here are the stats of my new Fireball :

DPS : 67,3 Cast Time : 1,06s

I have better gloves equipped, but my spell is less powerfull. These gloves are orange (Unique) and I do wonder if this is not just a small programming error, anyways, I hope you can explain this phenomenon, and maybe fix it!
Thank very much,
Frazic.

20% Reduced Cast Speed is a penalty , not a buff. If you cast slower , then your cast time will be higher , and so your dps is lower.

Logically yes, you do have a more powerful, but slower, fireball.

If compared to just per fireball, the new one will do much more. But factoring in DPS, that cast speed hurts alot.