The battle system for DoM is cumbersome and does not allow players to be responsive, i.e. canceling casts is extremely challenging when it shouldn’t be. As of now, the only method to cancel casts is to stay locked on target and push escape or enter before the spell is performed. If you decide to queue another action or select a different target, it is impossible to cancel your spell. In Final Fantasy XI, you could move to interrupt your own casts; in Final Fantasy XIV you have the freedom to move while casting, and it will not terminate your spell resulting in nearly all accidental spells going off.

Add a function/hotkey/command to cancel any casts; this function could also be used to cancel your entire command queue for accidental inputs.