High jump crit vs ghost

[Lunephx]

A while ago i was battling a loppuny and i saw a bug with high jump kick. Now being a fighting move, HJK should not be able to damage a pure ghost pokemon like coffagrigus who i was using at the time. However during a swap to cofagrigus from scrafty, HJK crit and proceeded to damage my cofa. To test if this was normal i repeated the swap again and for the instances of HJK that did not crit they did no damage to cofa as it should have been so the bug seems only to happen during crits.