Also, just change active into a basic one that drains 2 VE each loot box. (Example: Basic Sword, Basic Wu Tang Sword)
I actually figured out the remedy to the VE drain issue on my own by chance. Switching weapons by pressing W stops the VE drain because it forces the action of opening boxes to not use your active skill which comes with a VE cost. I suspect the game mechanics recognises opening boxes as an "attack" and that has a VE cost. This is more pronounced when we are using a high level active skills that quite possibly have a VE cost of over 100VE per cycle. This is also evident but less pronounced when switching to a lower VE cost active skill. The drain is still present, but less crippling. All that being said, this issue/bug still needs to be officially fixed by the Devs.
They aren't remotely comparable. Ozbudd demonstrates his video how to do it vs simply typing out how to do it - "Press W to switch weapons will fix VE drain". My post attempts to explain why it happens, why Ozbud's remedy works, what alternative remedies indicates about the nature of the 'bug', etc.
I don't think it's a bug tho. The Korean version is the same. If you're a melee users, and have active on, it will indeed drain your mana since it consumes mana every movement. Best thing to do is go in peace mode and loot boxes by pressing A and ofc turn off active.