diff --git a/app/static/js/services/soundfontPlayer.js b/app/static/js/services/soundfontPlayer.js
index b2ecae9..7931443 100644
--- a/app/static/js/services/soundfontPlayer.js
+++ b/app/static/js/services/soundfontPlayer.js
@@ -393,10 +393,13 @@
                     _fluidModule._fluid_synth_program_change(_synthPtr, ch, usedProg);
                 } catch (e) {}
             } else {
-                if (ch === undefined) ch = 0;
-                try {
-                    _fluidModule._fluid_synth_program_change(_synthPtr, ch, 0);
-                } catch (e) {}
+                // No instrument configured: use oscillator fallback directly.
+                // Do NOT call program_change(ch, 0) — FluidSynth would pick
+                // program 0 from whatever SoundFont is loaded (could be
+                // another track's SF), causing cross-track instrument leak.
+                var ctx = getCtx();
+                self._playNoteFallback(note, velocity, durationMs, startTime, undefined, null, channel, undefined);
+                return;
             }
             if (ch === undefined) ch = (usedBank === 128 ? 9 : 0);
             var ctx = getCtx();