Frazzle immunity message

Certain mobs are flat out immune to Frazzle' Magic Evasion Down effect. Yumcax and Gramsk-Droog to name two. When casting on them, it says 'no effect", which is peculiar because ordinarily when a mob is immune it'll say "completely resists". "No effect" is syntax used when a mob already has the effect present on them and you attempt to cast the same effect i.e trying to sleep a mob which is already slept. Even with Stymie it says No Effect. Perhaps this is a localization issue and it should instead read 'completely resists' like other spells when a mob has complete immunity? Or this may be a glitch. Not sure.