Why does the Ubuntu One client change the "modified time- and date-stamp" on the files after syncing? Syncing does not modify the content of the files!

I have a "working directory" for the files I want to sync (mostly OpenOffice-files). When done for the day, or when I quit working on that computer, I copy the files to the "Ubuntu One" directory, and Ubuntu One immediately starts syncing. When the syncing is in progress, I can se file after file change the time-stamp after the sync is complete. Why is it configured this way? The files are not really changed, and when I start working on one of my other computers, and sync the files there, I can't really know if the files had been changed on the time it shows. I try to use the Linux Ubuntu environment as much as possible, and when I found the Ubuntu One I quit working with Dropbox (it also works with Linux in general), but this use of time/date is so confusing that I think I must go back to Dropbox again, I can't use the both of them.

I have noticed one special detail: If I copy the files one more time, without changing anything in the file content, the Ubuntu One Client starts syncing again, works with the syncing just as long as in the first place, but then the files keep their original time- and datestamp. Funny!