This has been an issue for awhile for me now. I use click casting for most of my healing. Priest Purify works fine for click casting but on my druid and shaman, it will not allow me to bind either Natures Cure or Purify Spirit to click casting.
I am able to select the spell and assign it so a specific click-cast but then it removes it (and yes I hit save and don’t just exit the menu).
Edit:
One thing I noticed about both these skills is they have the same icon. Not sure if its an issue with the icon or the skills themselves.
Since Priest are in the same boat with Purify - I ended up having to make a macro like /cast [@mouseover] Purify and then bind that how I normally would do the spell you can switch them at the top of the click casting window between the macros and the spellbook until they fix it at least -.-
With my Priest, Purify works fine for click casting. Its just Natures Cure, and the Monks Cleanse ability (can’t remember its name) that won’t click cast.
I do notice that Natures Cure and the Monks ability both use the same graphic for the skill, not sure if that might be causing it or not.
Remove Corruption even works, which is the dispel for normal Druids. It’s only the Nature’s Cure version that Restoration Druids get that can’t be bound through click-casting, but putting it into a macro does work.