Why is it like this!!

Hello everyone, I have noticed recently, The immunity Doesnt work at all. I have used this many times and the members in the party still got status aliment.
Note: I have maxed

 

From: http://toramonline.com/index.php?threads/skill-tree-list-level-150.37578/

"12.) Immunity
Cast an aura to increase the party's resistance to ailments
Aura based party/self buffer
MP Cost = 500MP
Radius of Aura: 5 + Lvl/2 m (From caster as centre)
Cast Time = 2second (Affected by CSPD)
Effect: Generate an aura which gives ailment resistance to the party
Nerf on caster: Reduce ASPD%
Amount of ailment resistance given = 20 + lvl*3 % (Applied seperately from the ailment resistance % stat and MTL personal, as such can not be added to them to reach 100% ailment resistance)
Amount of ASPD% drop on caster = - (1000 - Lvl*75) %
Duration on caster = 15minutes
NOTES:
--All aura based support skills get removed if the caster is damaged (This includes 0 dmg from skills like perfect defense). The aura will stay if the caster dodges or evades however.
--All aura based support skills apply positive buff to party inside aura including the caster however the nerf is only applied to caster.
--Party members can get the buff only if they stand inside the radius of aura. "

It's only 50% resistance.