Icons moving to a different fence after saving / old items recognized as 'new'

I have configured Fences to save all new icons to a fence called 'New Items'. This works well and all new items that I create or new items I download are automatically moved to this fence.

I have another fence called 'Work Documents' where I keep several Excel and Word files. Whenever I work on any of the Excel or Word documents , save and close, the document (icon) suddenly automatically move to 'New Items' fence.

To me this behavior is erratic. I would expect the Excel and Word documents to remain at their original location after saving and closing, because these are not new items. They already existed on my desktop and have been there for quite some time.

Would anyone here have any idea on how to stop this behavior from happening?