It's in standalone mode - load up the app, play the keyboard for a bit (doesn't matter which preset) everything fine and dandy, then just cuts out audio on one channel after a couple of minutes. Only happens on Piano V2, none of my other V collection instruments...
I have tried with different headphones too, just to make sure it's not a hardware problem
I might just try reinstalling - though as it's happened on two different machines, am worried that I've just hit on a rare bug of some sort...