Look at the description of the vid:
Hujiko finally found out the truth: fatal bug made of Orbiter's skill "Dockhand" and "Riding weapon."
Its made out of two skills.
Ups on first page some1 else found this alrdy xD
However.. There is no logical way for the orbiter glitching the sorcs weap while having it on his inventory(maybe its made through attacking the sorc.. Maybe the skill riding weapon removes the weap of the enemy and maybe after that the weap is "glitched" lol)