diff --git a/src/engine/platform/genesis.cpp b/src/engine/platform/genesis.cpp
index 9a8bafc94..3ce422991 100644
--- a/src/engine/platform/genesis.cpp
+++ b/src/engine/platform/genesis.cpp
@@ -972,6 +972,7 @@ int DivPlatformGenesis::dispatch(DivCommand c) {
     }
     case DIV_CMD_FM_EXTCH: {
       if (extSys) {
+        if (extMode==(bool)c.value) break;
         extMode=c.value;
         immWrite(0x27,extMode?0x40:0);
       }
diff --git a/src/engine/platform/genesisext.cpp b/src/engine/platform/genesisext.cpp
index 56ae1ceaf..b901e2518 100644
--- a/src/engine/platform/genesisext.cpp
+++ b/src/engine/platform/genesisext.cpp
@@ -144,6 +144,7 @@ int DivPlatformGenesisExt::dispatch(DivCommand c) {
         opChan[ch].insChanged=true;
       }
       opChan[ch].ins=c.value;
+      chan[extChanOffs].ins=opChan[ch].ins;
       break;
     case DIV_CMD_PANNING: {
       if (c.value==0 && c.value2==0) {
@@ -219,8 +220,15 @@ int DivPlatformGenesisExt::dispatch(DivCommand c) {
       break;
     }
     case DIV_CMD_FM_EXTCH: {
+      if (extMode==(bool)c.value) break;
       extMode=c.value;
       immWrite(0x27,extMode?0x40:0);
+      if (!extMode) {
+        for (int i=0; i<4; i++) {
+          opChan[i].insChanged=true;
+        }
+        chan[extChanOffs].insChanged=true;
+      }
       break;
     }
     case DIV_CMD_FM_LFO: {
diff --git a/src/engine/platform/ym2203.cpp b/src/engine/platform/ym2203.cpp
index 68cccca45..02e92e191 100644
--- a/src/engine/platform/ym2203.cpp
+++ b/src/engine/platform/ym2203.cpp
@@ -670,6 +670,7 @@ int DivPlatformYM2203::dispatch(DivCommand c) {
     }
     case DIV_CMD_FM_EXTCH: {
       if (extSys) {
+        if (extMode==(bool)c.value) break;
         extMode=c.value;
         immWrite(0x27,extMode?0x40:0);
       }
diff --git a/src/engine/platform/ym2203ext.cpp b/src/engine/platform/ym2203ext.cpp
index 8bad13d48..675e85500 100644
--- a/src/engine/platform/ym2203ext.cpp
+++ b/src/engine/platform/ym2203ext.cpp
@@ -138,6 +138,7 @@ int DivPlatformYM2203Ext::dispatch(DivCommand c) {
         opChan[ch].insChanged=true;
       }
       opChan[ch].ins=c.value;
+      chan[extChanOffs].ins=opChan[ch].ins;
       break;
     case DIV_CMD_PITCH: {
       opChan[ch].pitch=c.value;
@@ -182,8 +183,15 @@ int DivPlatformYM2203Ext::dispatch(DivCommand c) {
       break;
     }
     case DIV_CMD_FM_EXTCH: {
+      if (extMode==(bool)c.value) break;
       extMode=c.value;
       immWrite(0x27,extMode?0x40:0);
+      if (!extMode) {
+        for (int i=0; i<4; i++) {
+          opChan[i].insChanged=true;
+        }
+        chan[extChanOffs].insChanged=true;
+      }
       break;
     }
     case DIV_CMD_FM_FB: {
diff --git a/src/engine/platform/ym2608.cpp b/src/engine/platform/ym2608.cpp
index 02a5ffa08..183533f81 100644
--- a/src/engine/platform/ym2608.cpp
+++ b/src/engine/platform/ym2608.cpp
@@ -1153,6 +1153,7 @@ int DivPlatformYM2608::dispatch(DivCommand c) {
     }
     case DIV_CMD_FM_EXTCH: {
       if (extSys) {
+        if (extMode==(bool)c.value) break;
         extMode=c.value;
         immWrite(0x27,extMode?0x40:0);
       }
diff --git a/src/engine/platform/ym2608ext.cpp b/src/engine/platform/ym2608ext.cpp
index 0801f0885..fae3a9157 100644
--- a/src/engine/platform/ym2608ext.cpp
+++ b/src/engine/platform/ym2608ext.cpp
@@ -141,6 +141,7 @@ int DivPlatformYM2608Ext::dispatch(DivCommand c) {
         opChan[ch].insChanged=true;
       }
       opChan[ch].ins=c.value;
+      chan[extChanOffs].ins=opChan[ch].ins;
       break;
     case DIV_CMD_PANNING: {
       if (c.value==0 && c.value2==0) {
@@ -200,8 +201,15 @@ int DivPlatformYM2608Ext::dispatch(DivCommand c) {
       break;
     }
     case DIV_CMD_FM_EXTCH: {
+      if (extMode==(bool)c.value) break;
       extMode=c.value;
       immWrite(0x27,extMode?0x40:0);
+      if (!extMode) {
+        for (int i=0; i<4; i++) {
+          opChan[i].insChanged=true;
+        }
+        chan[extChanOffs].insChanged=true;
+      }
       break;
     }
     case DIV_CMD_FM_LFO: {
diff --git a/src/engine/platform/ym2610.cpp b/src/engine/platform/ym2610.cpp
index 4fbf78595..5a1d80b58 100644
--- a/src/engine/platform/ym2610.cpp
+++ b/src/engine/platform/ym2610.cpp
@@ -1125,6 +1125,7 @@ int DivPlatformYM2610::dispatch(DivCommand c) {
     }
     case DIV_CMD_FM_EXTCH: {
       if (extSys) {
+        if (extMode==(bool)c.value) break;
         extMode=c.value;
         immWrite(0x27,extMode?0x40:0);
       }
diff --git a/src/engine/platform/ym2610b.cpp b/src/engine/platform/ym2610b.cpp
index 4fff47279..d65e50140 100644
--- a/src/engine/platform/ym2610b.cpp
+++ b/src/engine/platform/ym2610b.cpp
@@ -1192,6 +1192,7 @@ int DivPlatformYM2610B::dispatch(DivCommand c) {
     }
     case DIV_CMD_FM_EXTCH: {
       if (extSys) {
+        if (extMode==(bool)c.value) break;
         extMode=c.value;
         immWrite(0x27,extMode?0x40:0);
       }
diff --git a/src/engine/platform/ym2610bext.cpp b/src/engine/platform/ym2610bext.cpp
index 99727b734..98584f803 100644
--- a/src/engine/platform/ym2610bext.cpp
+++ b/src/engine/platform/ym2610bext.cpp
@@ -137,6 +137,7 @@ int DivPlatformYM2610BExt::dispatch(DivCommand c) {
         opChan[ch].insChanged=true;
       }
       opChan[ch].ins=c.value;
+      chan[extChanOffs].ins=opChan[ch].ins;
       break;
     case DIV_CMD_PANNING: {
       if (c.value==0 && c.value2==0) {
@@ -196,8 +197,15 @@ int DivPlatformYM2610BExt::dispatch(DivCommand c) {
       break;
     }
     case DIV_CMD_FM_EXTCH: {
+      if (extMode==(bool)c.value) break;
       extMode=c.value;
       immWrite(0x27,extMode?0x40:0);
+      if (!extMode) {
+        for (int i=0; i<4; i++) {
+          opChan[i].insChanged=true;
+        }
+        chan[extChanOffs].insChanged=true;
+      }
       break;
     }
     case DIV_CMD_FM_LFO: {
diff --git a/src/engine/platform/ym2610ext.cpp b/src/engine/platform/ym2610ext.cpp
index c35599fdd..979431d6b 100644
--- a/src/engine/platform/ym2610ext.cpp
+++ b/src/engine/platform/ym2610ext.cpp
@@ -137,6 +137,7 @@ int DivPlatformYM2610Ext::dispatch(DivCommand c) {
         opChan[ch].insChanged=true;
       }
       opChan[ch].ins=c.value;
+      chan[extChanOffs].ins=opChan[ch].ins;
       break;
     case DIV_CMD_PANNING: {
       if (c.value==0 && c.value2==0) {
@@ -196,8 +197,15 @@ int DivPlatformYM2610Ext::dispatch(DivCommand c) {
       break;
     }
     case DIV_CMD_FM_EXTCH: {
+      if (extMode==(bool)c.value) break;
       extMode=c.value;
       immWrite(0x27,extMode?0x40:0);
+      if (!extMode) {
+        for (int i=0; i<4; i++) {
+          opChan[i].insChanged=true;
+        }
+        chan[extChanOffs].insChanged=true;
+      }
       break;
     }
     case DIV_CMD_FM_LFO: {