Souler/TrinityCore — comment on commit 28ef56dbe46834799d8115dd692edd20d2f8cfd4
File: src/server/game/Spells/SpellMgr.cpp line 2991
By Souler:

This spell is trigered by mounts with TARGET_95, so targets the rider. But this spell itself has TARGET_95 too, so when you try casting any spell that trigger this spell will always return invalid target.