If you create a document and you associate a category to it, if you export the documents (acp) and reimport the document (acp) in another part por the same repository, you will observe that all the categories associated to the document are lost.
How to reproduce?:
Create a document.
Add a category to the document.
Export the document (ACP)
Re import the document in another part of the repository.
Categorisation lost in the re imported document.