With skill uses wrong weapon set

Hi,

every time i use the skill from the scelett storm mage, it changes to set numer II no matter which set i've bound to the skill

Things i tryed.
Un equip and reequip gem.
Unselect and reselet skill buttons.

Set Skill to set I, set skill to set II
Set Skill to both set.

The outcome is alwas the same.
Using the skill results in a weapon swith to set II

Evre other skill can be set to a specific set...

Sorry for my english, i am no native :)