Ah! Essentially it’s because the touch control with the mouse suck complete ass on MZ.
I would honestly advise using the keyboard when you want to build decks, the editor from there becomes much less clunky….
It’s an issue the card dev plugin owners do know about, but just a slightly complex one to fix currently. For now use the keyboard to make things easier for you (whenever they manage to fix the problem, I’ll be updating both the demo and paid versions with relevant fixes!)