using SC_POISON and poisoning time

[Tio Akima 74]

 Using SC_POISON and poisoning time

hi guys, i made an skill to poison the enemy after short / long range attacks

It's a passive skill.

When you attack an enemy, you have the possibility of poisoning it
I use SC_POISON to poison. (I put the check into battle.c)

but.... It poisons the enemy correctly (witch the correct duration), but if I try to poison the same enemy again, then the duration becomes bugged and disappears within 1 second.

Does anyone have any idea why this error?
my check in battle.c :
(with a 10% chance of poisoning)

if(sd){	
				// Checks whether the player has the skill or not 
				if(skill_lv = pc->checkskill(sd,ALL_POISON_PUNCH)>0){
					
					printf("have the skill");
					
					if( rnd()%100 < ( 1000 * skill_lv / 100 ) )
					{
						
						printf("came in ");					
						sc_start(src,target,SC_POISON,100,skill_lv,100000);
						
						
					}		
				}		
		}

Does anyone know why I can't poison the same enemy again?
(the poisoning time is bugged in the second poisoning)