I noticed today on my phone (Droid X running Android 2.2.1) that when streaming the Ubuntu One app would skip to the next song before the previous one had finished.
Looking into it, one of the mp3s downloaded from the server was only 2.5MB instead of 4.2MB as it shows on the server itself via one.ubuntu.com.
It's happened with multiple tracks today (I remember it happening once the first time I used the app too but shrugged it off as a glitch).
The app itself shows a star on the playlist item indicating the file was downloaded even though it was apparently cut off for some reason, perhaps lack of good cell coverage, or some sort of dropped connection. It seems like the latter may be happening and instead of showing an error or retrying it just stops and shows the download is complete.