this is somehow a technical issue.
Spell queue is working fine on spells that have more than GCD (1.5 s) cast time.
Still, for 1.5 second casting spells it doesn't work.
For example you can queue fireball into fireball, or fire blast into fireball, but you can't queue scorch into scorch, or fire blast into scorch.
This could apply to even queueing instant cast spells back to back, like moonfire spam or arcane explosion spam and so on.
Still, on 1.5 sec cast spells this is way worse, so we're back to spamming buttons in order to avoid dead time.
Is this intended for some reason?