Can't get rid of deafness ... bug or feature ?

In The black Pits, I have cast deafness on 10 radius with my Cleric to prevent the Thay mages from casting spells (with great success).

My Cleric was also affected by the spell.
I must confess I am not used of casting this spell ;-)

Even after resting, magical dispel, the effect (and icon) remains (fail at spell casting).

Is this a bug ?
Is the only mean to dispel this would be to drink the appropriate potion ?


Thanks for your answers.