Besides the global cooldown being set on the end of you casting a spell and not when you start it. I' have noticed that if you try to cast a spell in the middle of casting another spell while having the greyed client-side global cooldown animation on, it will redo this animation, it might be a missed packet or something? This might just be cosmetic, and since i get a serverside global cooldown at the end of my spell i cannot test whether it has any consequence to being able to cast a spell right after finishing another.
Example -> Cast 2 Second Spell -> 0,5 seconds before spell is done, and after global cooldown is done on the spell i recast the spell -> Clientside(atleast) ignores this but adds another 1.5 second global cooldown animation again, if this is just an animation or it also has an effect anywhere else, i do not know.
I know its alot client side, however since it doesnt happen on live im thinking somethings wrong packet wise :) Well use it if you can.
Okay maybe its something else. After reading abit of wcell code, it looks like global cooldown is handled by the same system as spell cooldown, the problem with this is that global cooldown acts differently than normal spell cooldown.
Global cooldown starts when you start casting the spell and not like the other type of cooldown, when you finished casting the spell. However Global cooldown is reset if you interupt spellcasting, this means you can start casting a fireball, move(cancel it), then start immediately after even though you just tried casting it.
Global cooldown is only reset if its a user dicision to interupt the spell or he is in some condition that doesnt allow spell casting, like if the target isnt infront of the caster.
Counterspell and other third party interupts does not reset the global cooldown of the target. (Also if he gets stunned while casting)
Also Counterspell is not affected by global cooldown and can be cast even while you have global cooldown. Counterspell also breaks the current spell being cast so that it can be more efficient. However Counterspell is still prohibited while under effects that doesnt allow you to cast spells.
I wrote about Counterspell so you can see some spells act differently with global cooldown.