Following up on Farnaby's post, I'm the creator of Decked Out. I'm happy to take a look at the code and see if I can find the issue. Is there a code repo I can look at?
The code for Decked Out is available on github, and if I had to guess I'd say the collision is in how we have both registered callbacks when shortcut is dropped on an image. The code for mine is in decked_out_events.lua in the onCardDroppedOnImage() function (which is registered with ImageManager as a callback when a shortcut is dropped on an image.
Having two registered callbacks doesn't look like it should cause any problems, but unless I can see the code for Spell Tokens I won't know for sure.

