Since 2 releases ago (May 11, I think), action buttons like Blizzard aren't lighting back up when the CD expires, they stay dark and apparently inactive but they can be used. The more recent release doesn't fix the issue so I've reverted back to the version before May 11 and the issue has gone away again.

I can't replicated this. Which spells experience this? Mine all seem to be returning to normal just fine after the CD expires. I don't have a mage to test with; if you can give me a druid ability that replicates this then that'd be helpful.

The change you're referring to was on line 138 of BUTTON.lua. I removed "self:UpdateObjectVisibility()" because it was screwing up drag and drop. On the surface the change seems to do nothing, but that was apparently wrong. The issue is that I can't replicate it.

Is this happening after a bar state change while the abilities are on cooldown, animating bling, or something else like that?

I wasn't able to find any druid abilities with the issue, most mage abilities are fine too except Blizzard and Frost Nova, both of those have the issue. I can't think of anything that's special about those two, either... anything I can think of, other similar buttons are fine. I'll check around on other toons to try for more examples.

I don't think those are factors.

I have noticed a couple of things: 1) When I disabled Cooldown Transparency the primary issue went away; 2) Doing that introduced another quirk that I probably just couldn't see before, those two abilities when the CD expires do NOT show the subtle light burst/sparkle on the button. I'm not sure if that sparkle can be toggled so not sure what would cause it to fire or not fire.

Hunter Disengage exhibits the same behaviour.

In theory I fixed this. Please test MASTER and see if it fixes your issue. I also added a bunch more drag and drop work to try to smooth out showing/hiding the grid when dragging and I fixed some other drag and drop quirks. If you guys think it works I'll push a new release

Testing now, I'll try to have some feedback before the weekend.

I think it's good, I haven't noticed the issue lately.