Frost ward and fire ward currently do not have priority when absorbing fire/frost damage from an enemy.
Ward spells should take damage before ice barrier takes damage. Currently the priority is based on buff sequence (ie cast ice barrier than frost ward → ice barrier has priority.) If, however, a ward is cast before ice barrier is applied, the ward will absorb damage first.
The correct behavior can be observed with mana shield - regardless of application order the wards will absorb damage before mana shield.
Other shielding spells should be investigated to determine interactions with wards.