From the help forum:
"have a problem with recording output from the virtual keyboard. it doesnt sustain. you know when you hold your finger down on a button and eventually when the on board cache on the keyboard runs out, the computer makes a rapid beeping noise? well it does that, like i'm pressing the button\note repeatedly, really fast, instead of just holding it down."
Solution proposal: The virtual keyboard in the tracker view does sustain properly. Take a look at this and apply the same functionality to the virtual keyboard midi device.