Okay this is kind of hard for me to describe but I will try and hope you understand. Before the patch, if I targeted someone and pressed a button that activates power word shield, it would put power word shield on them. They will get this debuff, weakened soul, that makes sure you can't power word shield them until the debuff runs out. If you would activate power word shield again, it would simply just not cast. Now after the patch when you power word shield someone who has the debuff after, the mouse icon thing starts to glow so you can click on another target. Is there any way to reverse this?
If it's glowing it's likely due to a talent or a glyph that's giving you something on the next cast. I didn't look at disc changes yet so I'm not sure what it could be but you're getting some sort of benefit (reduction in cost or something) if you cast it again is what it's saying. Check the buffs you have next to your minimap when the glow happens, and see if they're related in any way.
Hmmm I don't see it on Holy. Not sure what it could be. Maybe one of the tiered talents I haven't picked up that's shield related though I have Body and Soul and don't see anything. Or glyph? Like Spell Reflect or something?
I have submitted it as a bug and opened a ticket. I hope this can be solved because it's pretty annoying This even happens when I make a macro like: /cast [@target] Power word: shield.
It's most likely a game setting, I'm not at home so I can't look through them to try figuring out which ones it could be but check in there, Esc -> Interface -> Combat would be my first guess.