I have two Windows computers and a phone linked to my dropbox.
Last night, I went through sorting out my Camera Uploads folder and deleted lots of photos and moved everything else into various Photos subfolders.
At the time moving these files did not take much time at all, as your would expect because it's just changing the index.
According to the answer in this question,when syncing, Dropbox won't redownload files if you move them around in the Dropbox structure.
However, I'm now on my other computer, and it's telling me that it's downloading ~1000 files. Any idea what's caused this?