Thank you, DovEvl, for your reply.
As a note, I will not take credit for the code as it is originally the author of "Mazzle BC Spells!" who modified Mazzlefizz's layouts. I just made some minor tweaks to suit my tastes.
That being said, I understand what you're getting at. To be honest, I didn't realize that there was an issue with this particular button until I finally acquired an ability that was assigned to it.
The button to which Consecrate is assigned to is showing up just fine. I would think that if I changed the priorities and had the abilities, I could have Holy Shock or Repentance appear on that button. I tested this theory with a button that was already in place for Turn Dead. Which worked or I assume it did because now Turn Evil is in its place after Mazzification.
The problem, I suspect, is that the button that the layout is trying to assign Avenger's Shield to is not being reserved on the page and/or bar. I'm sure the crazy gnome would put the ability where the layout says the button should be ... but alas, the button isn't there so she discards that bit of code.
With that in mind, I do understand that troubleshooting this may be for naught should MazzleUI transition to a new Action Bar. However, I'm operating under the premise that if I want to keep this UI, I should probably learn how to maintain and modify it myself with the help, of course, of those with far superior coding skills and understanding than I.
I really do appreciate your attention on this matter and any more helpful insights or a nudge towards what I should look at specifically would be graciously accepted. =)