Deep Freeze is playing games with your files my good friend! Those temp files are quite big, and DF is convincing your computer that they exist when in all fairness they are being buffered in a temp directory.
If my memory is correct DF won't let you exclude folders from the process, hence you're going to get this problem you need to basically convince the program to ignore that folder, moving it to D drive is tricky as you'll need to exclude it. Try looking at Drive vaccine i use that and it has an exclusion drive option that you could place those dropbox temp files into and they won't be restored everytime.