Ok this has been bugged for a while now and I've reported it a few times.

An Illoke jarl lurches to his feet!
>incant 510
You intone a phrase of elemental power while raising your hands, invoking Hurl Boulder...
Your spell is ready.
You gesture at an Illoke jarl.
You hurl a large boulder at an Illoke jarl!
AS: +413 vs DS: +284 with AvD: +28 + d100 roll: +48 = +205
The stream of water washes harmlessly over the Illoke jarl.
Cast Roundtime 1 Second.



Some earth based elemental type creatures think 510 is actually 903 for some reason, it's not just limited to Stronghold/bowels creatures.