the mana cost/ mana loss reduction doesn't work on storm spirit ball lightning, this is true for fairy trinket as well, It only reduces activation mana for ball lightning not travel distance mana cost
Not a bug, it's one of the first line of the 7.36 patch.
only apply for initial cost.
There is even a small pop up example about ball lightning specifically
Item name
Kaya and Sange
Description
the mana cost/ mana loss reduction doesn't work on storm spirit ball lightning, this is true for fairy trinket as well, It only reduces activation mana for ball lightning not travel distance mana cost
Example Match ID and Timestamp
doesn't work all the time