I had a problem with the Uno, that it would skip notes if I started actually "playing" something.
The fix for this (and similar) problem is simple. Depending on your hardware, simply put some background music from your keyboard on and mute the volume of the music. This will keep a constant signal via the USB port.
I was kinda late to reply to this, but hopefully future users will get it to work like I did.
- Dids