diff --git a/wled00/FX.h b/wled00/FX.h
index fbdfe7c0..d52bcc2b 100644
--- a/wled00/FX.h
+++ b/wled00/FX.h
@@ -380,6 +380,7 @@ typedef struct Segment {
     };
     uint8_t  grouping, spacing;
     uint8_t  opacity;
+    bool needsBlank;              // WLEDMM indicates that Segment needs to be blanked (due to change of mirror / reverse / transpose / spacing)
     uint32_t colors[NUM_COLORS];
     uint8_t  cct;                 //0==1900K, 255==10091K
     uint8_t  custom1, custom2;    // custom FX parameters/sliders
@@ -489,6 +490,7 @@ typedef struct Segment {
       grouping(1),
       spacing(0),
       opacity(255),
+      needsBlank(false),
       colors{DEFAULT_COLOR,BLACK,BLACK},
       cct(127),
       custom1(DEFAULT_C1),
@@ -598,6 +600,7 @@ typedef struct Segment {
       * Safe to call from interrupts and network requests.
       */
     inline void markForReset(void) { reset = true; }  // setOption(SEG_OPTION_RESET, true)
+    inline void markForBlank(void) { needsBlank = true; } // WLEDMM serialize "blank" requests, avoid parallel drawing from different task
     void setUpLeds(void);   // set up leds[] array for loseless getPixelColor()
 
     // transition functions
diff --git a/wled00/FX_fcn.cpp b/wled00/FX_fcn.cpp
index 4a194d5c..e94e6e6a 100644
--- a/wled00/FX_fcn.cpp
+++ b/wled00/FX_fcn.cpp
@@ -277,7 +277,16 @@ void Segment::resetIfRequired() {
     next_time = 0; step = 0; call = 0; aux0 = 0; aux1 = 0;
     reset = false; // setOption(SEG_OPTION_RESET, false);
     startFrame();   // WLEDMM update cached propoerties
+    if (isActive()) fill(BLACK); // WLEDMM start clean
+    DEBUG_PRINTLN("Segment reset");
+  } else if (needsBlank) {
+    startFrame();   // WLEDMM update cached propoerties
+    if (isActive()) {
+      fill(BLACK); // WLEDMM start clean
+      DEBUG_PRINTLN("Segment blanked");
+    }
   }
+  needsBlank = false;
 }
 
 void Segment::setUpLeds() {
@@ -510,7 +519,7 @@ void Segment::setUp(uint16_t i1, uint16_t i2, uint8_t grp, uint8_t spc, uint16_t
 
   stateChanged = true; // send UDP/WS broadcast
 
-  if (stop>start) fill(BLACK); //turn old segment range off // WLEDMM stop > start
+  if (stop>start) markForBlank(); //turn old segment range off // WLEDMM stop > start
   if (i2 <= i1) { //disable segment
     stop = 0;
     markForReset();
@@ -2310,6 +2319,7 @@ void WS2812FX::restartRuntime(bool doReset) {
       seg.markForReset(); // seg.resetIfRequired(); // WLEDMM calling this function from webserver context will cause troubles
     } else {
       seg.next_time = 0; seg.step = 0;
+      seg.markForBlank();
     }
   }
 }
diff --git a/wled00/json.cpp b/wled00/json.cpp
index 7d355e79..28467a17 100644
--- a/wled00/json.cpp
+++ b/wled00/json.cpp
@@ -172,7 +172,7 @@ bool deserializeSegment(JsonObject elem, byte it, byte presetId)
   if (map1D2D != M12_jMap && seg.jMap)
     seg.deletejMap();
 
-  if ((spc>0 && spc!=seg.spacing) || seg.map1D2D!=map1D2D) seg.fill(BLACK); // clear spacing gaps // WLEDMM softhack007: this line sometimes crashes with "Stack canary watchpoint triggered (async_tcp)"
+  if ((spc>0 && spc!=seg.spacing) || seg.map1D2D!=map1D2D) seg.markForBlank(); // clear spacing gaps // WLEDMM softhack007: this line sometimes crashes with "Stack canary watchpoint triggered (async_tcp)"
 
   seg.map1D2D  = constrain(map1D2D, 0, 7);
   seg.soundSim = constrain(soundSim, 0, 1);
@@ -289,7 +289,7 @@ bool deserializeSegment(JsonObject elem, byte it, byte presetId)
   seg.reverse_y  = elem["rY"]  | seg.reverse_y;
   seg.mirror_y   = elem["mY"]  | seg.mirror_y;
   seg.transpose  = elem[F("tp")] | seg.transpose;
-  if (seg.is2D() && (seg.map1D2D == M12_pArc || seg.map1D2D == M12_sCircle) && (reverse != seg.reverse || reverse_y != seg.reverse_y || mirror != seg.mirror || mirror_y != seg.mirror_y)) seg.fill(BLACK); // clear entire segment (in case of Arc 1D to 2D expansion) WLEDMM: also Circle
+  if (seg.is2D() && (seg.map1D2D == M12_pArc || seg.map1D2D == M12_sCircle) && (reverse != seg.reverse || reverse_y != seg.reverse_y || mirror != seg.mirror || mirror_y != seg.mirror_y)) seg.markForBlank(); // clear entire segment (in case of Arc 1D to 2D expansion) WLEDMM: also Circle
   #endif
 
   byte fx = seg.mode;
@@ -386,6 +386,13 @@ bool deserializeSegment(JsonObject elem, byte it, byte presetId)
   if (seg.differs(prev) & 0x7F) {
     stateChanged = true;
     if ((seg.on == false) && (prev.on == true) && (prev.freeze == false)) prev.fill(BLACK); // WLEDMM: force BLACK if segment was turned off
+    else if (prev.isActive()) prev.fill(BLACK);   // WLEDMM fingers crossed
+    seg.markForBlank();    // WLEDMM
+  }
+  else if ((seg.grouping != prev.grouping) || (seg.spacing != prev.spacing) || (seg.transpose != prev.transpose)) {
+    // WLEDMM blank if grouping / spacing changed
+    seg.markForBlank();    
+    if (prev.isActive()) prev.fill(BLACK);   // WLEDMM fingers crossed
   }
 
   if (iAmGroot) suspendStripService = false; // WLEDMM release lock