Probably a sidetrack, but strange.
If I have the default the MS GS Wavetable Synt selected, and "use VSTi/DXi synt" ticked OFF, then he Melody track gets silent 2:nd time around when looping (all the rest of the tracks have sound all the time).
If I tick in "use VSTi/DXi synt" as ON, then the sound comes back o the Melody track and it stays on during looping.
(all the rest of the tracks have sound all the time).