Hi!
I think this is an incompatibility issue with the CharacterShowShadow.js.
I don't know how it works, but my guess is that it can be creating a fake character and sending it to the Sprite_Character to create a shadow. And that behavior is resulting the incompatibility.
If it is free, can you show me a link so i can download this charactershadow and take a look?
Also, try putting the character shadow above the Char Manager.