The phenomenon is, that the live played notes are not in time and/or dropped. The first recorded notes are replayed fine.
You can hear the same phenomenon.
Everything is fine.
The timing is fine and there are no drop outs.
It does not depend on the used softsynth. I've tested it with the fluidsynth and the whysynth plugin. It behave in the same manner.
The drop outs do not depend on the polyphony of the softsynth. The lost notes aren't cut off note because of a polyphony underflow.
There is thread called "Loop recording problems" on the user list which may contain some additional information.