The "lag" happened to me plenty of times, but that's because I was impatient and thinking "Why isn't anything happening" as I clicked it right before casting animation finished, which of course resulted me clicking it again, only to get Cleric's Stance bounce off and back on immediately. After I learned it queues itself and turns off or on after spell animation finishes I've been completely fine with it. No accidental switching unless I've been tired and forgot to switch it in the first place. :)
It's same as I can click Shroud of Saints when it's still greyed out while casting goes, and my character still does it after previous animation finishes and I'm already casting my next spell.
So what I'm saying; Cleric's Stance is fine as it is. Learn to queue it! :D
