I can't even begin to explain how annoying it is, when fighting multiple enemies, to have the 1st one die in the middle of trying to select a spell on the action bar, and then I have to refocus the action bar (since I have mine displayed 24/7) in order to continue attempting to select the spell, and then target the 2nd monster with it.

Or, you know, maybe don't force the action bar to lose focus/disappear immediately after the monster you're fighting dies. Maybe you need it for something. You don't know. Well, 9 times out of 10, I do need it for something, because I'm not just killing the 1 monster and then logging off.

This is honestly pretty annoying on other classes besides spellcasters, as well. At the very least, make it an option that the action bar doesn't lose/focus disappear after killing a monster, because right now, it's just kind of frustrating.