Azura's Star not working?

[FrozenWolf150]

I don't know if this is a glitch or if I'm doing something wrong. I'm running the GOTY edition with all the official plug-ins and both the Unofficial Oblivion Patch and the Unofficial Shivering Isles Patch, but no other mods. Anyway, I have Azura's Star in my inventory and I'm fighting Xivilai on the planes of Oblivion. I cast Soul Trap on them right before finishing them off, but when they die, nothing happens. Azura's Star remains empty and I never get a message that I captured a soul. I have other grand soul gems in my inventory, but they're all filled with souls of various sizes. I also have smaller soul gems, some empty, some filled.

Aren't Xivilai considered grand souls, and shouldn't the game fill Azura's Star before any other grand soul gems? I'm able to capture them in normal grand soul gems just fine, and this happens even when I have Azura's Star in my inventory. I can't seem to get it to work.

ETA: I just got it to work for the first time. I didn't do anything differently. I don't know why it's only working intermittently.

[Dark Spark]

Are you certain that, in the instances you used the Star, the Xivilai hadn't successfully absorbed your soul trap?

[Chicken Slayer]

I'm pretty sure that the game fills all other possible soul gems before Azura's star.

[Jeff]

Are you sure it was a Xivilani? Dremora are NPC, thus needing a Black Soul Gem. Xivilani are Daedra, but not part of the Dremora NPC Class, so it should have worked for them. However, as Dark Spark mentions, they do absorb spells.

[FrozenWolf150]

Are you certain that, in the instances you used the Star, the Xivilai hadn't successfully absorbed your soul trap?

How do you tell whether or not this happens? I saw the purple glow around them, indicating that the Soul Trap spell had hit. You're probably right though. It's just odd that it never happens with standard grand soul gems, just with Azura's Star.

[Jeff]

You still get the purple glow, as the spell did hit. You know it did not work, when You did not fill the soul gem. I am not being sarcastic, that is just the way it is. There is no way to tell, other than that. There is no text, as you would get, if the spell worked, but you did not have a soul gem large enough. Same as if they had Reflect Spell, no indication, except that you had a larger than normal health loss.