https://github.com/Electroblob77/Wizardry/blob/1.12.2/src/main/java/electroblob/wizardry/event/SpellBindEvent.java
So it would be the activate button also accounting for whats in the top right slot. So, if the spell in the top right that you were trying to apply to the weapon was higher level magic than your current magic level. Than the Arcane Workbench would not apply said spell to said weapon. (Could also account for if weapon is within level as well.)