Is this something new in 1.5?

So I raised a wolf from the dead. Then got tired of him before the spell ended and smited him. So he doesn't turn to ash... then I raise him again... kill him again... etc. Eventually kept doing it till my one hand went up because I was so close to leveling that skill anyway.

Haven't played since then. Some notes, I was using a staff of zombies that I found in random loot when I did it. I killed a wolf myself then raised it from the dead.

I did this very same thing inside of Dustman's Cairn a few days ago, with a staff of zombies. i stayed for quite some time just reviving then killing them till the staff lost its charge and i ran out of gems.

maybe that staff is bugged because i use the spell and everyone i raise, human or beast, turns to ash...dead thralls dont ash though

I believe this was indeed changed because ash piles were contributing to save game bloat. I thought this was implemented in 1.4 not 1.5 but I could be mistaken.

Reanimation spells cast from staves don't cause the body to disintegrate, I think this has been so from the start.