Archiving custom objects (Data mixing up)

Alright, hope I can explain this.

I have a NSMutableDictionary that constains custom "Lists". Each list as a name, color, and NSMutableArray of tasks. When I first add lists and tasks all s well but one the data is archived and unarchived all the objects in my dictionary still have their unique keys but they all point to the same object. (Or at least copies of the object) Either way they all contain the same data.

Example

Dictionary:

School -----> School (List Object)
Work ------> Work (List Object)

At this point I explore the list and all looks well.

Archived and unarchived......

Dictionary:

School -----> School (List Object)
Work ------> School (List Object)


Any help would be great.

Thanks