The relationships seem to be OK from my angle. The choices for Sub Category are filtering based on what Category is chosen, just like we want. Disabling the script allows me to choose any category/sub category available, and all the choices available when the script is enabled are in the entire list. Based on that I wouldn't expect it's adding new values, unless the act of filtering is 'adding' new values somehow.
Just to triple check, my lists are set up like this.
Category: Only one column, Title (type Text)
Sub-Category: Two columns, Title (type Text) and Category (Lookup to Category)
The current library: Type, Name, Modified, Modified By, Category, Sub Category.
Tried changing all references (and the list name) of Sub-Category to Sub Category but this didn't resolve the issue.
The only error in the browser is the unhelpful one that pops up when saving. (http://imgur.com/g2ewe) F12 tools reveals no additional errors clientside.
If by turning on debug mode you mean adding debug:true to the JSON object, this didn't add or change anything when I tried repeating the process.