I don't think it is a glitch. To activate the 2nd part you need to fulfil some conditions (plus some random chance?) although i haven't identify it all yet. It cannot be block nor shield.
There is no guide about it because nobody knows how to do it for sure but I have succeeded in consistently activating in during practice (Even if i really know how to it, i would not use it because it is reckless. 5B>2B>2C>5C>Arc Drive is way cooler).