The duration of this spell seems to be at minute / level. Also, even if dispelled (via dispel since nothing else counters it) the effect remains for the full duration.
Yeah, noted this too a while ago. It takes ages to wear off. We did finish the second half of the Granary quest (the part downstairs) while someone was hit by it at the beginning of this part and we had still to wait a while for it to wear off.
This spell is annoying when used on quests oh please oh please lessen duration