Official comment
Nick, see this article in the section that covers managing folders:
https://syncplicity.zendesk.com/hc/en-us/articles/201427490
To prevent all other users of a shared folder needing to download the data again, it is important that the person renaming or moving a folder first exclude that folder from synchronization. If the person who changes the folder name or location has editor rights to the folder or is the owner, then that folder will need to be downloaded again to any other user who is sharing it.