Seems UbuntuOne v184.108.40.206 does not analyze what part of a file has changed. It simply re-sends the whole file again.
(I have put a TrueCrypt file container, 128MB in the web storage from one machine, synched a folder on another machine. My container appeared there. I've mounted it, changed its' content - approximately few kilobytes, and dismounted my container. The HEX difference does not exceed several blocks, i.e. is much, much less than the whole container size. But UbuntuOne decided to upload the whole 128MB file to the web storage)
Is it by design?