Success rate of debuff

[yutio888]

After code diving, a subtle quession occurs to me. In many saving checks (e.g. knocking back, dispel good effects, ... and even some special debuff application) the success rate is bounded in 0% - 95%. However, when applying debuff, the fail rate of saving check is bounded in 0% - 95%, which means that the success rate is bounded in 5% - 100%. Is there any reason for this special case?