So I'm on my first play-through as a Mage, and I was awakened by a pack of wolves while napping in Wolfenwood. As they closed in, I used a sonic blast to stun them, but when I then tried to cast Fire Dart (my only actual offensive spell I'd been able to find by that point), right-clicking did absolutely nothing on any of the stunned wolves. As soon as they started to move again, I could cast on them, but while they were stunned, I could only run away.

I saw the same behavior with Entangle, and assumed it was a feature. It's a bit more sporting, and the spell is still useful to limit fights to one enemy at a time.

I wondered about that since I was attacking some stunned black molds up in Mistfell's North Coast. I wasn't sure why my spell wasn't working but assumed it was glitch with my computer.

Sounds like a bug to me.

Did to me, too, though I try to present things in a humorous manner.

Of note, I can't cast ANYTHING on a stunned opponent. There's no notification about "non-hostile" creatures and holding down the shift-key still doesn't let me cast on them (I tested this in case it was treating stunned creatures like generic NPCs).