Autoattack stops during skill global cd, wanted?

I will use the "Fireflies" skill for this example. But every skill you have that you can charge to a min. stack of 2 with a very long Cooldown (Fireflies has 30 sec cooldown) will do. You lock the skill to combatbar so the "overdrive" can be used. Start autoattack and use the skill 2 times in a row. You will notice that due to the very long cooldown the skill has, the global cooldown until you are able to do another cast also increases proportional to its base cooldown and the number of times you cast the skill. (red circle counting down)
During that time autoattacking is also stopped. Which in this example can take around 3 seconds. In that time the character is in full idle so to say.
I just want to bring this to attention. Maybe it is a wanted design. Very well could be.
On the other side it feels pretty clunky while playing.
There are arguments for both sides.

 

It might just be me but I think when my ferocious spider webs an enemy it also stops me from autoattack. Something is going on though.